Stawamus Chief is one of our most favourite hikes in Vancouver. I haven't been up there for at least two years and really missed it. It gets busy on the weekends but if you are going up to the 3rd peak, chances are, as soon as trail splits up from the main route to 3rd peak, you are probably going to be with just a few hikers on the rest of the trail.
3rd peak is longer and higher than both 1st and 2nd peaks but extra effort is definitely worth it! By the time you get up there and catch your breath, a beautiful view overlooking the valley opens up, and you can also see a crowd on the 1st peak :).
Just a note, when you get to the trail from Shannon Falls parking lot, there's a sign indicating that trail is closed. Map shows you an alternative route but this is misleading. The trail is actually NOT closed, just a small portion of it is. Go around the closed off area on the left side and you'll be on your way!