You'd have to have Napoleon beating England and reverting Quebec to Canada. Or Quebec revolts and becomes independent, France is wasted b the Napoleonic Wars and welcomes immigrants fleeing the chaos with land. In both cases replacing the English speakers. After Napoleon I don't think the French would have much interest in Canada.
Nope. That would be one way, but there are lots of others.
If you could bump the initial founding population of Quebec up, from the absurdly small numbers of OTL (something like 2.5-3k OTL), you could easily have an overwhelming number of francophones by 1840 (OTL's Union of Canadas) or 1867 (Confederation)
OTL, the 2 Canadas were forced together to try to submerge French Canada. If French Canada is overwhelmingly dominant, they won't do that.
If the francophones are overwhelmingly dominant, there's likely to be less Anglo immigration, and the Maritimes are less likely to want to join up to form a bigger Canada.
Now. How you get the founding population to be twice or four times the size, I don't know. One possibility would be to allow Huguenots to settle New France, but then you might not have the same 'revanche des berceaux'. (The Francophone population of Canada grew by some 3.5% vs about 3% for Anglos in the early years, and continued for much longer, partly due to the influence of the Roman Catholic Church.)
Another help would be if the Church didn't discourage people from moving inland (and out of their reach). If the French speakers had more heavily settled Upper Canada/Ontario, the United Empire Loyalists wouldn't have been so dominant there.