Settled on the banks of the Lachine Canal near the Atwater market, you will find this seasonal shop offering rentals for kayaks, boats and pedalos, as well as escorted outings and courses. I've used them a few times this year, including a kayaking course, and thoroughly enjoy it every time. The staff can be crabby but overall are helpful in answering questions and offering recommendations.
You can rent by the hour or sign up for a tour; the rates are crazy high, mostly due to its location and accessibility in the centre on the city, but you also have the option of getting memberships for the season which I'll surely do next year. The equipment is well maintained, and they provide you will all the safety equipment and guidelines before you head out.
I'm giving this venue four stars mostly cause I love the option of being able to rent a kayak and paddle down the Canal, all the way to the old port, in a moments notice. It's accessible and fun, and a seasonal membership is affordable if you intend to do this often enough.