The thing is, the Abenaki et all alligned with the US for a reason
I completely agree with the facts you put up, but as a optimist and a dreamer, Ii'm still not completely sold on the idea that its asb. 1) I'm sure that out of those 31,000 colonists, almost all of them either live on the coast or along the southern part of the Kennebec River. 2) What are the estimates on the native American population for the entire Wabanaki Confederacy? I'm sure its lower than 31,000, however from what I read, the Abenaki tribe alone had about one to two thousand people, while the Micmacs had a couple thousand, and I couldn't find any info on other the other tribes in the confederacy. 3)With a little bit of British help, I am sure they could have easily driven the Americans out of the frontier and to at least the coast. I also believe they probably could have taken out a few coastal settlements. Overall I have no doubt the idea is a long shot, but I think its possible.
Possible? Sure (almost anything is
possible, of course), but the thing is, the Abenaki et all alligned with the US for a reason, and, FWIW, the other tribal societies (Tuscarora, for example) that did so did "somewhat" better than their sister peoples who alligned with the British in this period...
And that's another point, the British were as quick to kick their "local" allies to the side as the Americans were, when it became useful; it's not like Tecumseh's people got anything out of their alliance with the British but devastation when the balloon went up the next time.
And as it was, as evidenced by the history of Maine and the various Anglo-American treaties over the US-BNA/Canada border, the US and UK always had more in common (in terms of creating and guaranteeing) a peaceful borderland than either did with supporting the other's potential "local" enemies.
The other issue in all this is that Europe (and, for that matter, the "Americans") had plenty of surplus population, and even northern Maine had resources Western settlers wanted, in the Eighteenth Century and afterwards; about the best realistic outcome for any of the tribal societies after 1750 or so are what amounts to larger and somewhat more secure reservations/preserves/etc.
And if the Americans don't force the issue, the British and BNAers certainly will; they weren't exactly gentle with the native peoples, historically, and for the same reason as the Americans - there was money to be made, and the tribal societies were (essentially) in the way.
Best,