St. Urbain Bagels are the best Montreal-style bagels in Toronto. While Bagel House may come a close second, nothing beats St. Urbain.
The sesame and poppy seed bagels are fantastic, as are the everything bagels. I usually try to get 4 of each for my dozen (totally $7.50). The St. Lawrence Market location usually runs out of everything bagels by the late-afternoon, but the Thornhill location is always full of all kinds if you are up in the northern part of the city.
When I lived in Los Angeles, I searched high and low for a bagel that would compare to St. Urbain. After a few months, I gave up my search. I started having friends bring three or four dozen when they would come visit, and my craving for St. Urbain was finally satisfied.