If you are visiting Montreal and have some time to walk around, one thing you can do is to see various pieces (and sometimes really masterpieces) of the wall painting and graffiti art.
Here is a slideshow which demonstrates just a small part of what one can find in the city:

Defining street art is tricky: It can range from historical statues to graffiti. Your question led me to discover Montreal's annual festival of murals (the city thrives on festivals so I shouldn't have been surprised.) Vivid examples, and plans for 2019, can be found here:
https://muralfestival.com/en/

Here's a blog from two years ago with locations from that summer, some of which may still be around:
https://www.mtlblog.com/things-to-do...o-and-see-asap

Southam, thanks for the links!
You are right: the term "street art" is very wide, I just did not want to complicate things in my post.
Some of the items from Montreal Murals are shown in my slideshow, however you can find a lot of interesting paintings in Greater Montreal which were not part of the festivals (and some of them, that are shown here, do not exist anymore).

I'm from Montral and Street Art is just amazing. There are real artists here and talent it's just a crazy. There are a lot of street art in the Plateau Mont-Royal but also some projections and other kinds of street arts in the Quartier des spectacles. Tere is a lot of activities there too!