I went seeking the best Montreal bagels while in Montreal and I believe Fairmont is the victor with an ever so slight lead.
You certainly aren't going here for the service, even when it's not busy you're about as important to the cashier as a watermelon in fruit ninja. They want you dealt with as quickly as possible so they can move on end of story. But, the next best option for Montreal bagels is about the same and perhaps a bit ruder.
First I recommend anything that's hot and fresh and second I recommend the chocolate chip bagels which have a cinnamon honey flavor (with chocolate... mmm).
When they are hot and fresh they don't need any butter or cream cheese... just eat it like a hot pretzel like they do as locals.
This place is 24 hours so I recommend trying to get here a little off hours. We got here at about 10pm, still found fresh stuff and had no one else in the store. It's obvious they deal with hoards of bagel lovers at certain times of day.