Unfortunately I find myself at various branches of Starbucks around the city far more often than I would prefer. I used to visit this branch fairly often because of it's incredible location, but now I avoid it like the plague.
Quite simply, it's just too crowded and the baristas move at a snail's pace. It's fairly small as far as Starbucks go. There is a small seating area in back, a couple tables in the walkway and a few more mixed in with the merchandise. Lines form fast and there isn't enough room to queue so people end up standing in the doorway and vestibule. During the winter, cold air sweeps straight into the seating area each time the door is opened destroying any potential ambiance. Once the weather turns nice there is a huge area for outdoor seating located just feet away from the constant rumble of traffic on both Guy and Maisonnueve.
There's not much to say about the food or coffee. It's exactly like every other Starbucks around the world. Not terrible and not great, not cheap and not expensive.