One thing to know about Montreal is the the city lives and dies by its nocturnal activities.  That said, the city learned long ago that any late night clubgoer needs that "end of night" nourishment.  Grease (the fat , not the musical) seems to be the food of choice for the Montreal late night scene.  Just walking down St. Lawrence Boulevard near the Prince Arthur cobblestone will give a good idea of what the city has to offer.  Popular eats include Pizza Madona's   $1.50 pizza,  the only pizza joint in North America where you can bargain for the price of the pizza.  Right across the street you can find La Belle Province ; if it's burgers, hot dogs and poutines you're after, this is the place to find it.  Also try La Banquise, reputed as the best poutine in Montreal.  It may be a little out of the way (994 Rachel est - between St. Denis and Ave Papineau, but a short and inexpensive taxi ride will get you there.  It's open 24 hours and is well worth it.  For people with more sophisticated culinary tastes, L'Express , a French bistro located at 3927 St-Denis, is open late  (the kitchen closes at 2 am) and is usually packed any night of the week, even at a late hour.  The Mecca of late night fast food however can be found a little further down the street.  Any visitor to Montreal can not leave without first trying Scwhartz's , great smoked meat sandwich and luckily it's open late.