The parks.

I don't know how it is in other cities, but in Montreal parks are central to many people's social lives. First, the summer is short and people want to spend as much time as possible outside while it's nice out. Another thing is that while you can't drink on the street, you can drink in the parks if you're having a "picnic" aka have some food. Even before weed was legal, it was a popular smoking spot too. And you can bring your grill and do BBQs in most parks. So on weekends, the parks are super full. People slacklining, doing circus stuff, jamming, having birthday parties, playing games etc.. It's not uncommon to make a group chat and inform/invite all your friends to a hangout. The weekly self-organized drum circle on the mountain is rumoured to have started back in the 70's. There's always larpers around there too. And there used to be a DJ playing at the gazeebo. I've met a group of guys playing brazilian vinyls on a battery powered tricycle-speaker setup.

It's a great low-pressure way to meet friends of friends, and just enjoy good weather. You can show up and leave anytime. Bring food, beer, a blanket and good company! I've had a couple days this summer where we "park-hopped" between 2-3 different circle of friends that decided to meet up somewhere outside. It's great :)