Whatever makes the Americans revolt will play a large part in what happens. Butterflies aside for the moment, say its abolition. The British abolished slavery in something like 1830 from what I remember. So either they make a special case for the Americans -being heavily agricultural in the south and that being a major part of the Empire's economy- until around or in 1848 when they force the Americans to likewise free their slaves, or maybe they abolish slavery in America at the same time and the resentment explodes in 1848. Well, with that, you're probably only going to have the South still with slaves and hence the South is going to be the only region with an axe to grind. Hence, its only a regional effort and I'm going to posit it'll collapse rather quickly. Taxes as an issue enough to push rebellion would likely get all Americans, but I don't know as if the Americans could pull it off and I don't know why the British would need to tax the Americans heavily. Hell, in the OTL the increase that led to revolution wasn't heavy, it was just that the Americans were used to paying near no taxes at all so when they did get taxed, they went into a tantrum (and this is from an American).