Please, do yourself a favour. Schwart's is alright as an "experience," I suppose but it hasn't been the same since Maurice Zbriger owned it. To me it's more of a tourist destination/Montreal institution rather than a place for a really good nosh. Celine Dion is a partner in it, FCS! The other owner is a Greek family that owns big chunks of Crescent and Mountain streets.
http://http://en.wikipedia.org/wiki/Schwartz%27s#History
Instead, try Beauty's. Not so much for deli as it is more of a classic diner. But, as we say, "Beauty's for breakfast."
http://beautys.ca/
As for deli, nothing in Montreal beats Reuben's right now. There are two of them, both on St. Catherine. One is in the basement on the SW corner of McGill College St. It's very basic and old-fashioned and you know it's genuine because it's open late Christmas Eve! The other is a large bustling place near Peel with a multi-page menu, ginormous cheesecakes in a glass display case and sandwiches so big you can barely get your mouth around them. The smoke meat cutters -- and this is a true art that, IMO, the guys at Caplansky's hadn't mastered when I have been there -- get it just right. It needs to be shaved, not sliced, and served up with just the right amount of spice-crusted fat.
To me, no visit back home is complete without a visit to both Beauty's and Reuben's
http://reubensdeli.com/
ETA: Incidentally, I always understood that difference between Montreal (and Manhattan) and Toronto in terms of deli culture was the origins of their Jewish communities. Montreal had a huge wave of Romanians (and east Europeans) who brought their smoked brisket-cuisine with them. Toronto was mostly Polish and north European. But I have never researched this so I can't say for sure.