A Montrealer took me and some friends to the best nightlife in Montreal within walk distance of our hostel: Bar St. Sulpice. With a different type of music on all of the four stories and a huge garden, there was no time to be bored!
Every person and website I consulted about Montreal told me to try one thing: a smoked meat sandwich from Schwartz. The line to eat in was pretty long, but we got it to go and enjoyed the neighborhood while we were at it. One of the best sandwiches I've had, well worth it!
Montreal is (kind of) known for its music and during the summer they have Picnique Electronique. Basically, it was a dance party on the beautiful Jean Drapeau Island. You could bring your own food and drinks and sit in the grass to take a break from the EDM. So much fun, would definitely go again if I had the chance.
PS: On the same island you can bike the Formula 1 race tracks which I didn't get to do, but is on the list for next time!