No, it would predict political division along racial lines, which is precisely what happens.

> The cleft in the US runs mainly between rural and urban populations

This is a weaker predictor than the racial demographics of the voters.

> high-diversity and low diversity areas

Are you using "diversity" as a synonym for "nonwhiteness"? Because if so, you're correct, but you could probably phrase this more explicitly.

> I hadn't noticed Toronto had become a hellscape of inter-ethnic conflict

Political rifts, which is what we are talking about, don't (usually, yet) manifest as visible ethnic conflict in the US either.