None of this answers my question. The Leafs and Habs have a deep animosity for each other in the sport that has, by far, the most cultural relevance in Canada. That's all well and good, but it doesn't make for an instant rivalry across all potential big league sports that could place teams in both cities.
Take Boston-New York in the States. In baseball, they have the fiercest, most historic rivalry in the game with Red Sox-Yankees. Patriots-Jets is a rivalry in the same way that the Roadrunner vs. Wile E. Coyote is a rivalry. It's one-sided and comical. In the winter sports, forget it. The Celtics and Knicks haven't given a damn about each other since John Havlicek and Willis Reed were playing. All the Bruins and Rangers have is the fact that they're both original six teams. Big deal.