I don't think this changes much regarding borders in mainland North America, the Spanish reacquired Florida OTL and it was eventually taken anyway. Florida itself might have a slightly different history, as the Spanish took a large number of Floridian natives and the paltry number of settlers to Cuba after the war OTL. Here there would be a slightly larger (but again, not by very much) "local" population, but I doubt that would deter American interests, as the Mexican Cession had a reasonable number of natives and Mexican settlers. I would imagine history plays out fairly similar here, with the USA capturing Florida while assisting in Mexico's independence war or finding a similar rationale around the early 19th century. The only way I see Spain retaining Florida is if it goes with an "Imperial Federation" idea making the Spanish New World too formidable an opponent, which I don't believe was particularly forthcoming.
However, I think British Cuba itself is more interesting to speculate about. During the ARW (I doubt British Cuba stops it), things may get interesting. The British don't have an excellent record regarding colonies with an established non-Anglo population, but were fairly pragmatic with measures like the Quebec Act, so something similar could happen here, and should obviate much interest in joining the Americans, since the Quebecois proved content enough with British Rule in OTL's war. However, the Quebec Act was historically passed by a fairly narrow margin and with Cuba there would be an undeniable racial component, which I doubt would help matters. A resentful Cuba could possibly join the ARW, and what happens there seems like an interesting thing to speculate. Cuba's success or failure in revolt probably depends on how much aid the Americans and allied navy's could sneak through, a motivated Cuban populace might be able to defeat land forces in the region, but I doubt it would be beyond British capabilities to hold down the island if it were a priority, Nova Scotia sympathized with the Americans OTL but was fairly impenetrable due to naval constraints. If repeated attempts failed, I could possibly see the British relenting if they couldn't get a decent foothold by war's end, though they may use it as a bargaining chip and doubtless would be loath to give up such a profitable colony, though by OTL's end part of the reason the British quit when they did was an increasing threat to their Caribbean assets. I don't think Canada is lost unless the Quebec Act fails, and even then Montreal and Halifax would not have been easily captured. I don't see why the Spanish wouldn't try to recapture the island, so it's possible they could get it back by end of the *ARW anyway. Continued British Cuba in these circumstances might not bode well for it, depending on how it was governed from then on, the British were responsive to the fairly small Rebellions of 1837 in Canada, so they may take proactive measures here to keep Cuba satisfied with British Rule. If that didn't happen, we may be looking at a history more like that of South Africa, and with likely American interest in supporting rebellion, this may be cause of continued poor Anglo-American relations throughout the 19th century, or beyond.
