We may also see an attempted Southern secession in the 1830s or 40s on abolition of the slave trade.
You mean abolition of slavery, not the slave trade. The South didn't have that much use for the slave trade by the end of the 18th century, which is why they accepted the U.S abolishing it.
A BNA is a tricky thing to accomplish, IMO. No matter which way you look at it, Britain will not be able to maintain colonial rule. By the 1760s, New France is no longer a threat, and the colonies are just on the verge of outstripping England in population. With the oncoming settlement of the Midwest alongside our already massive birthrate (Americans were having about twice as many kids survive to adulthood as their counterparts in Britain were) and immigration, this is only going to accelerate.
At this point, British rule now has a lot more cons than pros for the colonists. Things like the Navigation Laws were hurting the economies of all major american cities, especially New England (Why do you think they smuggled so much in the first place?). At the same time, the Thirteen Colonies were largely self-sustaining and eager to expand, which Britain wanted to prevent (not necessarily malevolently, but they certainly didn't want to fight their native allies, which American expansion would have led to). Without the threat of a New France, British military protection was no longer necessary in the American's eyes. America no longer needed Britain.
And if America no longer needed Britain, thoughts of independence will follow. Particularly among the American elite (you should know some of their names

), who had an almost insecure desire to be seen as equals by their peers in England. It's not like OTL's American Revolution was a bunch of rednecks shouting "I H8 taxes M8!", there were severe social and economic factors pressuring for independence. Add to all
this that America was already developing its own way of ruling itself, and they handled themselves fairly well, thank you very much.
So I think that only an even more liberal version of "Home Rule" is possible in the long term for a BNA. BNA would either have to be like middle 20th century Canada (independent in all but name) or Brazil (A colony ruling the mother country). Demographics, economics, politics and culture all agree with me.
On to the actual question: The Americans will still settle at the very least the midwest, probably more. British attempts to protect their native American allies are not going to last long after colonial militias have destroyed them.
I'll say this now: During the 7YW, immigration to Ohio had already begun, and it was picking up the pace fast. The proclamation of 1763 was something that made the American Revolution inevitable, IMO, and any TL with a surviving BNA will have to avoid that. Once colonists flood in (and they will, Americans were used to having lots of free land and once that was gone in say, New England they went for the midwest), the Indians are screwed long term and the British empire will slowly but surely become the American one.
Going into smaller details: it would be interesting to see how the British parcel off land ITTL. OTL's Township system was fairly effective, and I could see something very similar developing ITTL. It would also be cool for some of those grandiose claims by states (didn't Massachusetts of all places claim land in Minnesota?) to come into being. That's highly unlikely, of course. In fact, BNA is highly unlikely.