Please take this as rank speculation steeped in fantasy.
The peoples of the western provinces have more in common with the US cultures just below them than the provinces have with the central government in Ontario.
The Canadian federal government denies the provinces sole possession of their own mineral resources.
The irritation of treating Quebec as if it is somehow endangered while forcing English speakers outside Quebec to accept French, then letting Quebec actively discriminate against Anglophones, becomes a catalyst for breaking up.
If Canada were to break up, look for the western provinces, BC, Alberta, Saskatchewan and Manitoba to join the US. Ontario would remain as the nation of Canada along with the Northern Territories. Quebec would break off to become French Canada, probably taking her trading partners, the Maritimes, with her.
Or maybe not. Without transfer payments from the rest of Canada, Quebec might be too economically challenged to administer the provinces east of her. In that case, the Maritimes, unable to survive economically on their own (they’re a basket case now) would petition to join the US. The US might not want to add to her number of dependent states. It could get interesting.
Western Canada is ready to gp now. We bring the world’s largest supplies of oil and natural gas and agriculture, mines and forests.
We have the people with the right spirit (for the most part), let’s get this done.
The Canadian federal government denies the provinces sole possession of their own mineral resources.
I don't know if this is true. Having lived in western Canada and done business up there, I can only remember dealing with industries like logging and oil/gas that dealt with the provincial governments. One of the great advantages of NAFTA, in fact, is that it prohibits the Canadian government from getting too heavily involved in any of their industries up there.
As you correctly point out, the natural trend over time has been for Canadian provinces and regions to trade more freely with their southern counterparts than their Canadian neighbors. I don't see that changing anytime soon, unless it's the U.S. (not Canada) that pushes to change it.
The central government of Canada is not in Ontario. It's in Ottawa. It's similar to the District of Columbia.