Keep in mind at the time Ontario and Quebec were called upper and lower Canada respectively. I agree Lower Canada May keep the name Quebec, but Upper Canada likely becomes just Canada. Alternatively they could easily remain Upper and Lower Canada.
The original borders of the Canada's would likely be the state borders, I disagree with hzn5pk that what is modern north Ontario would become Indian Territory. The Province of upper Canada wasn't as big as modern day and if the Americans do purchase Rupert's Land [which could become Rupert's Territory] the trail of tears would have already happened, with the Canadian Natives being added in.
Everything outside of the original borders of upper and lower Canada would be Rupert's Land, owned by the Hudson's bay. I might be able to see this become American if the Americans offer enough for it, but the British North-Western Territory [Modern Yukon, NW Territories, Northeast Nunavut mainland and Northern Alberta] would be unlikely. It is desolate, and the Americans wouldn't accept any price the British demand, hell, it's doubtful that the Americans would even want it.
At the time, Nova Scotia was OTL New Brunswick and Nova Scotia, minus Cape Breton ,which would be added onto NS in 1820. ITTL, The British likely keep a hold of Cape Breton and PEI and they likely become provinces of the Dominion of Newfoundland. The Labrador dispute probably doesn't happen ITTL, the dispute originally started as a result of a poorly defined border of the Labrador Coast. This timeline likely see's the UK being more clear and Labrador remains as is.
The Treaty of 1818 still happens, with the British marking off Rupert's land from the US, but the border in Oregon county might be in favor of the British. One of the deals for the sale of Rupert's Land might be the British Claims to the Columbia River Border for British Columbia. The British North-Western Territory is transferred to British Columbia and we likely see a Dominion of British Columbia. Likely featuring a later name change [Mackenzie, Fraser, Columbia?] While the British Arctic Territory is likely transferred to Newfoundland.
Manitoba would still be a province, though it might remain smaller than OTl, closer to it's original borders. and the Prairie Provinces would be likely different because there were many proposals for the division ranging from one super province, to 4 small ones. I think that due to American standards on State populations, we might see a single super province. This America would likely still have Mainland Territories, Keewatin from modern north Manitoba and Ontario, and Unguva from Northeast Quebec
The Americans would likely admit Texas as multiple states to attempt to balance the Slave-Free states. But the Civil War would likely still occur.