Mile-End Park is fun. Rosemont Park is full of the absolute worst "cool-guy" kooks. Despite the park having potential the locals completely ruin this park. The parks in 'burbs are better than the parks in the city, but then you get traditional suburban crowd.
Place de la Paix is a must visit spot. The ledges are higher than one might expect.
In terms of food, Momo Sushi is pretty hip and tasty (even if it is vegan). Ma Poule Mouille is great for the price (the park across the street has a few spots as well.) If you end up in Hochelaga 3 Pata Poufs has great sandwiches that are super cheap. And, Croissant Croissant is fucking amazing. Best place for coffee and a pastry.