Grumans is the real deal.
I lived for a few years in Montreal and used to go to Ben's. Grumans is much smaller, but the food is terrific. They claim the best Reuben in town, which is true. May be the best in the West.
The burger also looked quite good. Grumans is now in the regular rotation. Next up is some Montreal smoked meat.
If you want a great deli experience in Calgary this is your place.