1. Quebec likely WOULDN'T just revert to its 1763 borders but instead likely be its 1791 Lower Canada boundary lines with one exception. Why? This is because 1) the USA wanted natural borders at its start (look at the Rainy River boundary in what is now northeastern Minnesota, or the St. Croix River of eastern Maine, besides the obvious Mississippi River and Great Lakes) and 2) watersheds and rivers will be the most useful boundary markers in the Canadian Shield's frozen and forested wilderness.... and Lower Canada in 1791 stretched north to the Hudson Bay watershed instead of that weird, straight, arbitrary 1763 north marker line. Its western border would still be the Ottawa River (its a great western border when Quebec cedes western claims to the government with the other states) and its southern border as OTL/1783, but its eastern border may revert to the 1763 St. John River in Labrador and the Labrador watershed otherwise per convenient geographic boundaries for the "USA wants natural borders at first" note. Geographically this is still huge in square miles even if it looks far more 'even' compared to the other states than it did in 1774, even if the population huddles around the St. Lawrence River valley.
2. Nova Scotia and PEI (here still St. John Island) remain as in OTL pre-1783 - Nova Scotia holds *New Brunswick and SJI its own colony - simply because if Nova Scotia goes Patriot then there's no division between the American settlers of *New Brunswick that got swamped by migrating Loyalists who then disliked the older, uppity settlers of Nova Scotia Proper - they're ALL Patriot/American here and no Loyalists have moved in! SJI remains separate because if you didn't merge Delaware with Pennsylvania or New England together, then merging SJI into Nova Scotia reeks of hypocrisy and sets a bad example for tiny states' continued existence.
3. Most of the West Indies are way far-off, and the only Patriot-settler-holding colonies were Bermuda and the Bahamas. They're pretty easy to be their own states in spite of their size because, again, they were separate colonies in the first place. Heck, they can help offset the States of *Canada (as local Americans and Qubeckers alike called that province), Nova Scotia, and St. John Island in the Senate and House alike.