Glad to have one of these in the west island but it seems to be unmarked from the outside? I was with my brother who already knew it was there but you really can't tell it's there until you walk up to the door. It's located in a small squat commercial building on the 'southeast' corner (it's technically due east but you know how Montrealers always think of the island as a bit shifted..) of Brunswick and Tecumseh. There is a parking lot and the store entrance is closest to the parking lot entrance off Tecumseh.
Anyway, you can watch fresh bagels being made on one side, and there is a café on the other. It's a large and clean space. I find St-Viateur bagels to be a bit thicker than Fairmont but they are still good. Several different kinds but I'm not sure that they always have them in stock (sesame and poppy are always available though). Eating a fresh bagel is the best bit if you're bringing them home to freeze, be sure to let them cool fully before putting them in the plastic bags that come with the paper ones!