It's still unclear to me what is the most popular greasy spoon in town, but in terms of age, no place beats Montreal Pool Room.
Established in 1912, a lot of stuff went down in this place. Located on what used to be the most dangerous street corner in town, it still maintains its reputation as a seedy late-night eatery—without actual creeps, thanks to the rejuvenation of the neighborhood and its evolution toward becoming the Quartier des Spectacles.
The specialties: steamed top-loaded hot dogs and, of course, poutine, with tons of cheese curds.
Also, despite being called a "pool room," I have yet to see a pool table, or anything related to pool for that matter, in this establishment. But I guess I'm willing to forgive this nonsense for an extra cheese topping on my poutine.