Can I wet vent a laundry sink?
What size should the pipes be to be code in Toronto?

This is something you should check with local building department. The codes can change from town to town. The local rules could be stricter then county or country.

Chuck

As Chuck said, you'll need to check with the local plumbing jurisdiction to be 100% sure. What fixture vent are you tying the laundry sink into? You probably can't connect into the vent for the washing machine, but almost any other vent is OK as long as you are on the same floor...;)

Mark