Ok, I'm cheating...Beaubien Bagels isn't in Longueuil, it's in Montreal. But, they make the best bagels in Montreal, and it's a quick drive across the Jacques Cartier Bridge to get to them from Longueuil.
Located on Beaubien, near St. Hubert, Beaubien Bagels makes their bagels by hand. Before being baked in an open, wood-burning oven, the bagels are first boiled.
The prices are reasonable...we got two dozen bagels for around $11.00, and their variety is incredible! In addition to the usual poppy or sesame seed, you can get blueberry, chocolate chip, onion, all-dressed (or "everything"), cinnamon-raisin, and more.
If you like bagels, you'll love a Beaubien Bagel.