It's important to keep in mind that much of the hinterland of North America was not settled, still densely concentrated on one eastern coastline or another.
In a TL where Québec and Ontario remain united, and where there is no Loyalist settlement in the 1780s to leapfrog over a frontier of settlement that wouldn't reach the Great Lakes until the 1820s, I think it entirely possible that Canadiens spreading upstream from Montreal might be the first to settle Ontario before the Anglo-Americans.
They could, but I'm not sure they could remain a majority in the OTL Ontario region. I could envision anglophones eventually coming to outnumber them there, causing the state of *Canada to eventually be split up, as Massachusetts was (with Maine seceding) in 1820.
Likewise it is not ASB to have an ITTL Quebec Act which rather than (which was an exception to the rule at the time) try and keep the French Canadians happy, it instead treats those people like the British treated the (Catholic) Irish at the time. Under such a law it would be far more likely that the French Canadians join the fight against the British.
That could provoke a reaction from France. The 1763 Treaty of Paris stated that "His Britannick Majesty, on his side, agrees to grant the liberty of the Catholick religion to the inhabitants of Canada: he will, in consequence, give the most precise and most effectual orders, that his new Roman Catholic subjects may profess the worship of their religion according to the rites of the Romish church, as far as the laws of Great Britain permit."
I guess the last part ("as far as the laws of Great Britain permit") theoretically offered Britain some flexibility, but it would be contrary to the spirit of the treaty to seriously persecute the Canadiens over religion.