You're right about the larger population base deterring English settlement. That probably would have happened if more young, eligible women had been drawn to New France to marry the trappers. Then they would eventually settle down and concentrate on raising kids; in OTL the men outnumbered the women, so the men spent most of their time trapping and exploring. That was part of the reason why Montcalm lost to Wolfe - the French were outnumbered to begin with. I think if, post Revolutionary War, there were more French in upper Canada, the Empire Loyalists would be prone to settle more in the Maritimes, and York Peninsula (w/Toronto, etc. is). Thus there would be no Eastern Townships, and probably few if any English in Montreal. Also if English guarantees of French law and preservation of Catholic faith in New France after Wolfe bests Montcalm are more ambiguous, you could eventually get enough support for a successful armed rebellion.