Montreal is a super nice city. Where are you exactly? If you're looking for skateparks, take a look at this website. It lists all the parks in quebec
If you're into rock climbing, there's this pretty sick bouldering place called bloc shop. Its like 17$ and you can go all day
Like he said, there are a bunch of festivals all summer long and most of them are free as well which is always nice. Also bunch of cool bars which all close at 3am. My favorite is probably TRH because theres a skate bowl and a halfpipe inside.
Skiing wise, theres a bunch of hills to choose from, bromont is one but its a bit further from the island itself. Avila has one of, if not the best park in quebec and it's pretty close from the island. Tremblant is also pretty nice but a bit on the more expensive side. I heard the park is also really nice but I can't really speak for it.
Hope this helped. Hit me up if you have more questions.