The American revolution was a fundamentally different war to 1812 though.
There Britain saw itself as the bad guy, it was a massivly unpopular war. When France joined the war sympathy for the Americans vanished (they were no longer nice Brits fighting for liberty and all that, they were arch traitors alliged with the high anti-democratic evil) but things were too far gone.
With 1812 it was the Americans trying to unjustly conquer Brits who wanted to remain free. The strategic loss of Canada may be somewhat acceptable but abandoning British people would not be. Britain owns the sea, it could let the American economy fall to bits then pick up the pieces later.

This misses the point. There wouldn't be a war if America owned Canada. Just theoertically speaking assuming Britain wakes up one day and decides to invade the US.
There's no way America stands a chance of gaining the west indies- both politically and militarily.
There Britain saw itself as the bad guy, it was a massivly unpopular war. When France joined the war sympathy for the Americans vanished (they were no longer nice Brits fighting for liberty and all that, they were arch traitors alliged with the high anti-democratic evil) but things were too far gone.
With 1812 it was the Americans trying to unjustly conquer Brits who wanted to remain free. The strategic loss of Canada may be somewhat acceptable but abandoning British people would not be. Britain owns the sea, it could let the American economy fall to bits then pick up the pieces later.
The only ASB thing here is saying that that a US victory in these conditions (having all of Canada at the start) would be such. If (going beyond the present PoD) the War of 1812 would begin with America alreeady owning all of Canada, it would be for Britain at the very best a compelety frustrating long stalemate. They would lack any foothold in the continent, raids and naval blockades didn't gain them anything IOTL and in ARW, with a mcuh weaker stalemate. At best, they would not gain anything, at worse, they could lose major chunks of the British West Indies (precious colonies that the USA would very much gain, thank you), depending on how much good or bad the US Navy is during the early period of the war.
This misses the point. There wouldn't be a war if America owned Canada. Just theoertically speaking assuming Britain wakes up one day and decides to invade the US.
There's no way America stands a chance of gaining the west indies- both politically and militarily.