Large parts of the United States would be territories controlled by France, Spain, and possibly Russia, for a lot longer, if not into today (you can’t really predict how far a knock-on effect will go through history). There would probably be more American Indians. One of the British policies disliked by Americans was the ban on westward expansion into the Ohio River valley. A British win over the Americans allows that policy to be enforced longer.
It would also depend on WHEN the Brits gain victory - before or after the Americans gained their alliance with France?
The possibility of an additional revolution when Britain outlaws slavery is there, but it would depend on how they did it. I am not very familiar with Britain’s legislation against slavery (beginning in 1809, I think). Total, instant abolition would definitely cause trouble. Banning the slave trade, and then transitioning to abolition gradually could probably have been managed. But since Britain and France were at war, it’s possible that Napoleon might have had agents/troops in North America causing trouble much earlier. There might have even been a little Napoleonic sideshow on this continent, given the presence of British, Spanish, and French interests. There’s the potential gain of the Louisiana Purchase (or even some of it) as terms in a peace deal in 1815.
Maybe Napoleon flees St. Helena for Louisiana and his 100 Days last a lot longer this time around…