I assume the Irish and the English going to a French North America would have learned French, the same way the ones going to the Argentine learned Spanish - and the way the non-English speaking immigrants in our timetrack learned and adapted English.

And there'd probably be a sort of Anglophone equivalent of French Canada down the East Coast.

I suspect that there wouldn't have been the same degree of separation between the music of black and white Americans as this developed. My impression is that, on the whole, for one reason or another, French colonists have tended not to be as consistant and dedicated in their racism as English colonists. That could have mean both loss and gain musically.