By the time of the Seven Years' War it is already far too late; at that time the British population in North America vastly outnumbered the French population, to the extent that when they fought the British in that time-period the French regarded it as a victory even to keep what they had because they understood just how badly the odds were against them by that point.
Personally I would go with a 17th-century PoD. For most of the 17th century the English (not yet British—the Acts of Union hadn't happened yet) didn't even have their northern and southern colonies linked. Early in the 17th century you could quite possibly have one of the two main English colonial areas (i.e. New England and the South) be taken over outright by one of the other colonial powers, as England took over New Netherland in OTL; with such small populations it would be fairly easy. With the English threat decreased, then you just need France to adopt a more English-style method of colonisation (that is, relying more on European settlers displacing Native Americans, rather than on alliances with Native Americans and limited European presence which is the ultimately inferior strategy France pursued in OTL). There are plenty of people who have come up with plenty of ways to do this: one of the most commonly mentioned is the idea of making French America a place for religious dissidents—specifically Huguenots—as English America (and later British America) was. The seigneurial system almost certainly has to go.
