Canada: Freelancing while on a work permit?

I am in Canada (Montreal) on a work permit with a specific company. I do some light freelance on the side with a couple companies back in the States, and now an opportunity has presented itself for a small project here in Canada.

My question, and concern is…is it “legal” for me to do freelance work while on a work permit? Do I need additional clearance before this is possible?

Thanks for any input!