I like it, but one query: If the British held the south, surely they'd be less inclined to ditch Florida in the Treaty of Paris?
A prid pro quo for the Spanish ditching their support The revolutionaries. I am assuming they are still able to occupy parts of the West Florida coast as with OTL. East Florida is closer to their main possessions in the Caribbean and they still hold New Orleans to control Luisiana. thus for evacuating the West Florida coast and leaving the War against Britain they regain East Florida. This prompt slightly settled Georgia to leave the C.C. shortly after which helps to bolster the British in the south centred in Charleston. Tarleton has been reigned in and is not ranging high and low all over the south after Green or another Patriot leader.
Stalemated in the south the Patriot forces concentrate on re-linking up New England and Virginia and the mid-Atlantic states. Which were separated after the successful three pronged attack on Albany this time around. By 1882 though the revolutionaries have finally been able to recapture it and reduce the control of the British in NY to the Champlain valley. New York and lOng Island and the lands of the Iroquois in the west. The Iroquois (all of the six nations)in this TL have rallied to the British. Hence the reason for the "Niagara region" still being in shared control between the US and Britain.
The initial disposition of the entire NW beyond the Ohio River, south of the Lakes and west of the treaty line of Fort Stanwix with the natives is an area of Joint occupancy at the peace. Something in the long term that is untenable but suffices for that time period...1783. The harsher terms and the harsher political climate in the lead up to the the declaration of independence ( which is the POD in Nth Am that I am working on for now) leads to a stronger loyalist migration settling in the south in Georgia and West Florida and in the North in Vermont/N.S. Quebec and Newfoundland.
With the initial successful campaign of the Brits in the north securing NY. loyalist regiments that form do not base along the St. Lawrence They are in the Mohawk and Upper Hudson/Champlain Valleys instead. Fr. Cdn militias instead are used to secure the St. Lawrence West of Montreal to L. Ontario and at Detroit. Hence the Ethnic line in Quebec in the aftermath is somewhat further west than OTL to the valleys of the South Nation river and the Upper Rideau in what is Eastern Ont OTL.
By the mid '90's Britain is preoccupied with the French revolutionary threat and a compromise with the US is necessary. While they have not been pouring into the lands of the Iroquois they have been spilling over to the lands of the upper Ohio and those beyond the Appalachians in Virginia and North Carolina building upon the fledgling settlements established during the ARW. A compromise is necessary as conflicts between American settlers and the natives ( mostly Shawnees and Miamis )is growing. Blue Jacket is actually offered protection in this TL in the aftermath of an alternate Fallen timbers because of the more entrenched Br. position in the NW. With War threatening, and Britain not wanting a War in Nth Am given the concern over the continent The Jay treaty compromise results. the Ohio district becomes an area of exclusive US influence, and Britain Michigan as a prid pro quo. Both would have liked the Niagara but neither would like the other to have it and the further districts are not of immediate interest in the '90's for the US and the Brits still want to preserve them for the Natives. Both districts are still integral to the "NW area of Joint occupany" there is no annexation by either, jhust a recognition that these districts should considering circumstances on the ground be areas of pre-eminent influence for each respectively.
Eventually this is going to lead to unilateral annexation of the Upper Ohio by the US in the '00's. It will be this TL's version of the War of 1812. I am thinking that it would not go overly well for Britain given its likely pre-occupation on the Continent....then again I haven't decided how things go on the Continent yet and how Pre-occupied the Brits will be.
Initially I think that such a conflict will likely end with a final partition of the NW to avoid such a disaster again. the US obtaining Illinois and the Niagara and annexing the largest part of Vt and SC.. reconstructing them as US states..and leading to a second loyalist migration. Obviously the annexation of Ohio is recognized. This assumes that the US concentrates on Militias as OTL but they are larger in the south as well as the North. Britain with the aid of the Natives does well in the West and of course in Maine. The disruption of trade leads to disaffection in NE for the War Effort despite its gains but it does not gain enough momentum to become significant force until the aftermath of the, for lack of a better name..."The Ohio War" or "2nd war of Independence" . I figure this will give the US a significant win and boost to its prestige and will force the Brits to re-evaluate the needs for defence in its western territories ( namely the lack of settlers to formalize their presence) They are also going to want to tred lightly with the natives. The Iroquois Nations will migrate with the 2nd loyalist migration. Settling in the Grand river Valley of Michigan in TTL instead of the Grand River Valley of Ontario in OTL (these areas having already been settled by loyalists instead in the wake of the 1st ARW.
thats as far as I'm at until Europe shakes out.
In short even if the US was restricted in the aftermath of the ARW to something less..It is still likely to grow in some measure from those beginnings. Its all a matter of when or if they meet an impenetrable force. Either military or political.