Kosher restaurants in Montreal are fantastic! Basically, Queen Mary Rd. has all the kosher places that you want to visit! (Exodus, Expressti, Chez Benny) So get off at the Snowdon Metro!
For inexpensive there are:
Pizza Pita - (its the place to see and be seen on sat nights when its open till 4 am and has a drive-thru!) they have tons of dairy and veggie food options, even a drivethru! located on Decarie Blvd, after Van Horne.
Chez Benny - Really authentic Israeli style shwarmas and shish taouks in pitas and lafas. They also have an awesome Chinese menu. (on Queen Mary, next to the Snowdon Metro)
Exodus is great - has sushi as well as your typical Israeli meat and fish dishes, great smoked meat sandwiches (the place to go with a family when everyone wants something different). Expressti is on Queen Mary, but across from Decarie, right near the residential side. Try the grilled chicken salad.
Yakimono (formerly Makmomo) has great sushi, possibly the best kosher sushi hands down in North America. If you love sushi, you must try this place out! (they have really cool desserts too!) To get to Yakimono by metro, get off at Villa Maria and turn left as you walk out of the station. To get there by car, from Van Horne, head south along Decarie Blvd, turn left on Monkland, then turn right onto Decarie Street. Not too bad in price - rolls range from $5-10.
Expressti is a small but chic place near Exodus (on Queen Mary, between Decarie and Clanranald) that has dairy - paninis, salads, soups, coffees, great desserts, sushi. Try the italian panini at lunch, and for dinner, the french onion soup, the salmon teriyaki salad and a piece of mocha cheesecake. One of my favorite kosher cafes! Btw - the place is rather small and gets crowded on weekends, so call ahead to book a table!
Exceptions - similar to Expressti, but also has an amazing French bakery. Next door to Chez Benny.
Ernies and Ellies - Chinese/North American cuisine, this place is where families go when they are celebrating a birthday or an occasion (go for one of the table d'hote specials which are usually about $15 for four courses). This one is inside the Decarie Square mall.
El Morroco - this is downtown, on Drummond. Authentic morrocan food, quite pricey.
The Y cafe - in the YMHA on Cote St Catherine - have both dairy and meat.
If you're downtown and need a quick bite for lunch, there are two places - on Peel, the Chabad house which is dairy, - on Stanley, the Hillel house, which is meat.