Lot of "ifs" don't you think?
Two of them: New France holding to some degree for long enough that France isn't totally expelled from North America by the time the war ends in Europe, and France winning one of the various naval battles which it could have won IOTL if it had had better luck on the day. That doesn't strike me as enormously implausible, especially if we alter the situation on the Continent (Frederick the Great was pretty lucky too) to make things there go less well for the British, so they're able to do.
It doesn't have to be the Seven Years' War either; that was just the latest Anglo-French war where the French had a significant presence in North America. We could go earlier; indeed, the earlier we go, the lower the existing population imbalance, the more plausible it is for an Anglo-French colonial conflict to go the other way.
Look, as significant as the deployment of "European" troops (or the lack thereof, in some conflicts) was to the ultimate collapse(s) of the European empires in the Western Hemisphere was, the foundational question of which "settler" society (English-, French- or Spanish-speaking) was going to dominate the continent was going to turn on population in North America, and the basis for that was who ended up in charge of the termperate Atlantic coastal zone (call it New Hampshire to Georgia); the answer is self-evident.
Best,
I am unconvinced that the British settler population advantage was as decisive by the 1750s as you are saying it is. A victorious France and a later more populated New France, coupled with French-backed and French-armed Native Americans gradually becoming more adept
vis-à-vis European settlers, may keep the British settlers confined to the east coast, especially by political pressure on Great Britain via victories in Europe; before the American Revolutionary War, British America (as it then was) was not a state of its own which could wage war against other European colonies unaffected by the success or failure of its colonial master. That would still probably leave the Anglo-Americans (presuming that they are united) as the most populous and richest state in North America, but not necessarily dominating that continent as they do today.
And the Seven Years' War is the latest possible choice, with the highest imbalance; the earlier the war we pick, the weaker the English/later British position relative to its European rivals was, the easier it is to imagine the English/later British hold in North America being weakened or even expunged entirely like the Dutch hold.
I presume you wouldn't say that the 1590s English hold in North America was destined for domination of that continent, though you say that the 1750s British hold in North America was. I'd be interested to see where you would draw the cut-off point.