I think the assumption of hostility is not well founded.
The American revolution in the 13 colonies OTL involved about a third of the population being actively Patriot, about a third being actively Loyalist, and a third just keeping their heads down and hoping any shooting would happen elsewhere, keeping their options open to either side winning.
My reading up on the status of British organization of the colonies north of the OTL 13 indicates that actually in 1775, there were really just three--Quebec, recently greatly expanded to include the Great Lakes and the whole swathe of territory south of it between the confluence of Mississippi and Ohio rivers, on to the Proclamation Line along the Appalachian ridge reserving land west and north of it for Native people (but now under administration centered in Quebec, which is beyond the Proclamation line, the Francophone subjects being in effect treated as Native people). Newfoundland, just the island and other close ones, with the two French islands of St. Pierre and Milequon excepted--these islands remain French overseas territories to this very day, and vote for a seat in the National Assembly. And Nova Scotia was given the rest; Prince Edward Isle, originally renamed St Johns Island, was the first to be broken away from Halifax administration as a separate colony, during the ARW--it got a lot of Loyalist refugees who would indeed be hostile, but also a lot of Scottish immigrants who, the Wikipedia article on PEI's history remarked, were freer to be Gaelic Scots than in Scotland. New Brunswick was broken out of NS administration in the immediate aftermath of the OTL ARW, as more Loyalists from the lower 13 former colonies settled there.
Whereas I specified that the effective POD for the USA incorporating the Maritimes would in fact be greater success in the several expeditions sent north very early in the conflict--in 1775 in fact--at taking Quebec, Montreal and the Maritimes--in effect, Nova Scotia.
Now overrunning all of Nova Scotia would be impossible, since Halifax would as mentioned hold out pretty well, but there is little reason to doubt the political demographics of Nova Scotia before the above-mentioned waves of settlement by Loyalist refugees and Scots in PEI would be radically different than that in other New England colonies. Which is to say, lots of Loyalists to be sure, but that was true in Massachusetts or Virginia; didn't stop the Patriot faction from dominating there. I think you are projecting modern Canadian patriotism backward; Canada's identity is in a big part "we aren't Yankees," but prior to the crises of the mid-1770s there was nothing to distinguish Nova Scotians, or Newfies for that matter, from other colonies in rebellion. Newfoundland is indeed a tougher question because the British control all access to it with a much stronger sea power; the USA has essentially none beyond some roving privateers. Such a privateer by the way did seize power in PEI for a time, later in the war than I suggest the necessary turning point in the north would have to be; this would be after the anti-Rebel faction there was much strengthened. At the point I think would be the necessary POD, neither PEI nor New Brunswick exists as a major settlement, and the action in NS would be east of there, and essentially political with small reinforcement of NS people inclined to the Patriot way of seeing things for the same reasons people in New Hampshire or Connecticut or Rhode Island were. All New Englanders sharing the same broad concerns the rest of the New England colonies, or rather their Patriot-inclined sectors, were.
So in Nova Scotia at least, the issue is not hostile Yankee occupiers, it is whether the ability of British reinforcements allied with local Loyalists can overwhelm the latter's own compatriots or not. My guess is, surely they can hold on to Halifax itself and some zone around it, and the Loyalists will concentrate there and the Patriots flee that zone, splitting NS into a British occupation zone and a Patriot controlled larger (but not very populated) hinterland.
The hostile population to be subdued there is not the whole NS population, it is the hard core Loyalists, and this was a problem the Patriots faced down throughout the 13 former colonies.
What is especially problematic is that OTL, the safety valve for tens of thousands of the most compromised Loyalists was to flee into what became Canada, in large part as far as its Anglophone roots go, founded by these very refugees. In this ATL, the title implies Britain is swept from all footholds in North America and lacking detailed direction from the author I assumed this would be thorough. Now we are told Newfoundland does not go to the USA, which weakens the implication of the title somewhat. But to be sure, Newfoundland as defined in 1774 did not as the province and formerly unfederated colony did OTL after the post ARW reforms, include mainland Labrador--that was under the Province of Quebec as expanded in '74. Even if, in the course of the later war endgame, the British do retain hold of control of Labrador (and having lost control of Quebec's Francophone center, presumably annex it to Newfoundland sort of like OTL but probably with somewhat different boundaries) thus retaining a North American continental foothold, anything north of the divide between the Great Lakes and Saint Lawrence watershed and the great northern shield which is very poor farmland and very sparsely settled to this day is at some comfortable remove. So even Rupert's Land can remain firmly in British hands, and it is more viable with Newfoundland straddling the sea passage to Hudson's Bay from the Atlantic, and with Newfoundland serving as a viable base of operations to break up the length of the sea transit from British harbors to those in Hudson's Bay.
I admit that seizing those two zones was a stretch for American diplomacy especially bearing in mind French ambiguity.
And perhaps, if the USA makes no attempt to incorporate Rupert's Land and Newfoundland, it might make more sense for the Americans to mollify and involve their French royal ally by giving them back a truncated Quebec--rather a truncated New France/French Canada, splitting the far western claims around the Great Lakes and south of there, the USA taking the part of recently expanded "Quebec" between the southern lake shores and the Ohio-Mississippi system, France getting as what I suppose they would either revive the name of New France or use the name of Canada for, the French settled core, the lands north of and between the Great Lakes and Saint Lawrence, and as far down the Saint Lawrence as French colonists had actually settled, leaving the USA to gain essentially just Nova Scotia along with the southern part of the far western lands. The advantage to the USA of letting France gratify her pride, resume rule of her own nationals (1763 is still quite recent in living memory) with their own laws and religion, is that the French cannot reasonably hope, with access to the larger reaches of New France to the south and west now under Spanish control impeded, to refight the old rivalry wars to seriously threaten the US; US population has grown too great for a reasonably affordable New France based expedition to prevail, even given they would likely get much help from the Native peoples. Reviving New France around the core of what the British were calling "Quebec" before 1774 (
map here) and partitioning the additions south and west would interpose a strip of French territory between British Rupert's land, and give the French an interest in maintaining sufficient naval force to maintain access past the gauntlet the British based on Newfoundland might seek to impose. France would be strong enough to maintain security of territories granted by the treaty mainly by deterrence--Yankees attacking in greed for more land to drive Native people off of would risk facing hostility of both Britain and France which would be most costly and perhaps fatal, but as long as the USA keeps hands off French claims, New France is not an existential threat nor likely to give the Yankees causus belli.
However I think the author will insist on the USA holding Quebec. And being able to do that militarily was exactly what the northern colonies in rebellion thought they could do in 1775, and of course they had the example of the (posthumous) success of Wolfe in the former war ended in '63 to guide them. I think it is reasonable to suggest that militarily controlling Quebec and Montreal was within the reach of the Patriots, limited as they were, especially if Nova Scotia's hinterland is won over to the Patriot side.
The Francophone Quebecois, as it happens, were not much discontented with British rule, which was undertaken rather shrewdly. And Native people would tend to side with the British Loyalists too. But I do gather from reading up on the expedition that the plan was to present Yankee occupation as "liberation," and presuming military initial success, to deal in good faith with Francophone regional authorities and offer a square deal, which might besides reincorporation with the Kingdom of France, also include the option of Canadien independence as an allied republic--or conceivably even a monarchy, making some deal with the Bourbon king of France for a cadet line of that dynasty to be settled there. As noted, if the US negotiators are going to allow the French foot in the door they might as well just advocate for full restoration of New France (in limited boundaries) to bring the power of France in as a doorstop against possible British revanchism based out of Newfoundland and Prince Rupert's Land.
So assume instead that Francophone elites can in fact see their way to advantages to being included in the US federation, as an autonomous state with "republican form of government." The Anglo-American Patriots are unlikely to insist on radical democracy of course; if the Church and landed elites want to restrict their "republican" electorate and persons with standing for high office, that's not out of line with what other states among the 13 might attempt.
It may indeed be important to make a special stipulation in the Articles, exceptional from general policy--in general the Articles included one stating citizens of one state could settle in any other and become naturalized citizens of their new state on the same basis as someone born there; a special reservation to the Quebec state government to control settlement might be quite acceptable, considering that everyone understands that Quebec Francophone society is quite different than the broadly similar to one another former British Colonies. In fact one effect of offering the Quebec Francophone elites a good share of good land to the west, limiting what the Yankees insist on taking as new territory for new states to be settled later, would be to give a safety valve to Native peoples, for while the natural increase of the Francophone Quebecois was pretty high, the French had a greater affinity for making relationships with Native people, whose populations were imploding due to ongoing decimation by plague. Instead of filling such territories as the OTL southern Ontario peninsula, the southern peninsula of Michigan, and the Wisconsin territory west of Lake Michigan with descendants of habitants of the old Canadien core, various tribal peoples fleeing Yankee expansion into Ohio and points south and eventually west could be settled there, gradually intermarrying with French people to basically turn the large territory into a Metis society. Note that instead of simply annexing all those western lands to Quebec, that state can be formed immediately with fixed boundaries, but a section of the western Territories held collectively by the USA reserved for Francophone expansion and Native settlement, to eventually form two or three new Francophone-Native states. Again these people, in this scenario US citizens, are a bit thrown under the bus in that they face the British in Prince Rupert's land directly--but it would not be easy for Britain to stage a powerful revanchist comeback conquest attempt out of that sparsely populated and distant center! Incorporating present and future Francophones in the US system would give them access to resources in lieu of French controlled ones, governed by a Federal government they participate in, and armed as well with the powers the Constitution conceded to states.
US Patriot leadership tended to be strongly drawn from former colonial elites--less so that Loyalist, but not by a lot; most of the Framer names we tend to read in history books were big shots socially before the Revolution and even more elite in the Patriot reframed society during and after it. Why assume Quebec's leadership, the luminaries of their new state, would be less cultured? Elite Canadiens under British rule had to become proficient in English, and as I noted, elite Anglophone Colonials knew French as a prestige language. Quebec's 4 or so Representatives and two Senators, assuming the Constitution as we know it is not butterflied away, would be of the classes fairly comfortable doing business in English, and when for reasons of pride or manuevering they insisted on "reverting" to French, many Congressmen and Senators from Anglophone America would be able to follow them. Inclusion of Quebec in the USA from the beginning would surely reinforce the status of French as a key language for ambitious persons to learn, as it would encourage Quebecois Canadiens to become fairly good with English. Just as Quebec/Canada (still haven't settled on the name, bearing in mind "Quebec" only referred to the area around the city of Quebec in French administrative practice, naming the whole giant province Quebec was a British idea and quite a novel one in the 1770s) will be a place where the main official language is French but English will be frequently spoken there--even if special provisions in the Articles prevents Anglophones from gaining full state citizenship status, still a lot of business opportunities will bring Anglo-Yankees in to base themselves there, in Montreal or in the back country--so the frontiers near Quebec will hear French spoken quite a lot and Anglo-Yanks will learn it widely, for grassroots pragmatic reasons as well as for reasons of pretensions to high culture. In the Articles period, France is likely to remain a valued ally and the business of various committees of Congress Assembled will be preoccupied with various French relations. Assuming Canada (that is, the Francophone state) is settling more and more integrally into the Union, by the time (assuming minimal butterflying of either US or French developments) the new US Constitution forms, coincident with the French revolutionary crisis, Canada is settled in, integral to the new Constitutional order, and its likely dominant elites will be quite horrified at the revolutionary developments and quite glad to be independent of France as it goes radical republican. More or less Old Regimist refugee emigres from France will be quite welcome to settle there and in any Francophone-reserved territories.
Again, I do suppose some explicit rights to control Anglophone immigration into Canada and perhaps some reserved northwestern territories with an eye toward future Francophone statehood will carry over from special provision in the Articles to special provision in the Constitution, perhaps in as laconic a form as a clause stating as the Articles did that all US citizens have a right to settle in any state or territory "except as established law subject to Congress shall direct." This may also carry over to it becoming standard procedure for Native peoples driven off their lands to have rights of refuge in these northern reserves and Canada, where they might usefully be fitted into a French-speaker directed system of integration.
Of course they have good reasons not to, but they are off to the side, and if the Patriots back in '75 and '76 have brains, they will offer the Canadien elites good inducements that will serve them well in the balance of power, and developing events in France will take care of any regrets they have not having angled for reunion with France. Historically OTL, British administration of Quebec/Lower Canada was canny enough to avoid setting off land mines; it is a question of whether on the whole having their own state and perhaps some special enumerated rights (mainly to be left alone with a decent sphere of development reserved for them and Native allies) is overall a better deal for the ruling elites than remaining subordinated to the British system. My reading of online histories of Quebec uncovers some serious humiliations the "enlightened, canny" rule of the Francophones by the British retained well past the Revolutionary period--they could well be objectively better off, with a purely French common law, their own republican in form state government they control, and special rights to control citizenship to keep Francophone control and perhaps be in a position to keep state promises to settled Native peoples taking refuge there. There will of course be no War of 1812; it is interesting and a bit dismaying to think how the upcoming slavery crisis might boil over without the safety valve for escaped fugitive slaves to enter Canada here, but in the first few generations overall the situation might prove far more peaceful in the new USA, at least in the north--expansion into Spanish and Mexican territory seems likely to be a major thing of course, especially with the USA not having to watch its northern back.
The USA actually does not have much of a history of "official language only" in general governance; English prevails by heavy inertia and default. In specific contexts of course, we have had a quite nasty heavy hand trying to break people of other languages, notably in school policies and against Native people, also I gather a nasty anti-French campaign was conducted in Louisiana (in IIRC the 20th century) and of course German speakers got a lot of grief in the WWI years and after. I think once again you are projecting culture wars of the 20th century back on the 19th, which was pretty laissez-faire; which is not to say no oppression occurred (it is part of American mythology that the market is God and can do no wrong, and private is always kinder and better than public) but that it happened by private means, which is typically American--where other nations might use uniformed troops for ethnic cleansing say we would rely on state militias and vigilante groups; we do a lot of violence others do in formal guise privately.
So, with exceptions in places where large numbers of people persisted in allegiance to a non-USA "white" culture, we haven't had blanket "speak English or else" policies promoted by formal government.
The US Federal Government is most certainly not going to get involved in trying to ban French outside of Canada. State governments might, but I think they would pay a political cost for demonstrating such bigotry. As noted, French is a prestigious language of high culture in English speaking nations, especially the USA. And rather than tit for tat resentment at Canada favoring French as primary official language, but surely also providing fair levels of service in English, I rather think bilingualism would be a grassroots thing more extensive than OTL; even far from direct Canadien contact, various political and social factions will find alliance with this or that Canadien faction fashionable and this will tend to promote the spread of more or less proficiency in French, and in some places evolution of "Franglais" in various forms, all over the country. Assuming the USA eventually does get ahold of the New Orleans area, the Francophones of Louisiana might find the ATL USA much more accepting of that state also retaining a major or perhaps ongoing majority Francophone practice.
Why the heck not? Aside from my guess that French will be widely known among primary English speakers, and English pretty widely understood in Canada and perhaps other Francophone states, there is this thing you may have heard of called "translation." Every legal document must be written in one language anyway, why not simultaneously make another copy in another? It is not like we are asking USAians of an English language persuasion to produce translations in flawless Mandarin or Sumerian after all; English and French have a long history of close contact and around 1800 it was deemed more or less the standard tongue of European diplomacy. People like Thomas Jefferson could personally write what they have just written in English in good French on the spot; Benjamin Franklin was obviously proficient. I forget if it was Paul Revere's father or grandfather who was a Huguenot refugee-settler in Boston, but I believe the Patriot leader was fairly good at French himself--and while widely respected, he was definitely not in the city's intellectual elite, rather he was a leader of artisans and other working class people--not as grassroots as Sam Adams, but overlapping--in fact a historian I have read identifies Revere as remarkable in his ability to penetrate all the social levels of Boston and Massachusetts. He was of course an anti-Papist and might have been less civil than others if actually dealing with the kind of people liable to be running Canada state, but he'd be dealing with them in their own language. And again in a pinch, many Canadiens would be quite capable, those who were literate anyway, of parsing out English documents too, and writing their own translations for more expert verification and correction.
I see no impediment to every legal document put out by the Federal Government to be published in both English and French, which would also come in handy reaching more Native people. Surely Canada State would be under some pressure to produce English translations of their transactions too, and provide recourse accommodating English speakers fairly across the board (though perhaps setting a certain level of proficiency in French as a requirement for full citizenship voting rights, waived for Native peoples operating through the network of Native alliances). Neighboring states, or anywhere in the Union attracting many Francophone settlers or having such populations of their own such as Louisiana, would have the templates for setting up a decent degree of French language accommodation ready to hand.
Surely some will remain bigoted against French as a language, but I rather think that will come to be seen as the mark of a barbaric and crude mind in US circles. Many more might remain bigoted against the Catholic church, or particular factions of Franco-American society--democratic republicans would be hostile to Canada's favored old regimeist elites, while conservatives and reactionaries might despite a countervailing insurgent party of hoi polloi
habitants and
Metis asserting their rights and standing as citizens of an increasingly democratic-normed set of republics. All these bigotries might mix and match, but the one barrier I expect to fall without anyone mourning it is the language barrier as everyone tends to be more proficient in both languages.