The BEST place for Montreal Smoked Meat Sandwiches, is Schwarz's deli, on St. Laurent Street ( I think ) in Montreal. It is the place that has defined the Montreal Smoked Meat experience. The deli is very small, but has been around for over 70 years. They manage to serve their huge demand, by piling many groups of people together at the same table, and outputting massive amounts of take-out orders. Still their is always a large lineup at Schwarz's.
Generally a proper Montreal Smoked Meat Sandwich is a HUGE pile of deli sliced smoked meat, piled between two slices of rye bread with mustard. If you ever go to Schwarz's, don't bother ordering the lean, the only true way to experience a Montreal Smoked Meat Sandwich from Schwarz's is to have it Full or Medium Fat.
A friend of ours brought us there when we went to Montreal to visit her. I've never had a better sandwich in my life. If anyone you know is going to Montreal, definitely get them to bring you some smoked meat, and some rye bread.