It's a little to the west of Montreal itself, but I recommend Smoke Meat Pete's for some fantastic smoked meat or some goooood ribs. But since it's Montreal, if you have to pick one or the other, try his smoked meat
It's about ... 20 minutes west of downtown Montreal by highway. Well worth the trip out there, in my opinion, but your time may or may not work to head out that way. Very casual place. Heck, you order at the window and then take a seat
If you can,check out Au Pied de Cochon on Duluth. Crazy restaurant and if you can snag a seat at the bar you won't feel out of place dining alone.
Schwartz has good Montreal smoked meat if you're not into driving.
If you go with Au Pied de Cochon, call them up and book a reservation. I made the mistake of not making a reservation and couldn't get a spot when I dropped in, not even at the bar - and that was just a Tuesday evening, if I remember correctly.
I second the recommendations for Au Pied de Cochon and Schwartz's. Both have excellent food, are quintessential Montreal experiences and are great for single diners (Schwartz's has communal tables and APdC has an eating bar in directly in front of the open kitchen).