We rented from Harbourfront Canoe and Kayak. They have singles and doubles (tandem) which is what we rented.
If you are interested in doing it but don’t want to paddle across the harbour, you can actually have them boat you across and you can start from the islands. Crossing the harbour can be daunting, you have to make sure you stay out of the restricted area near the Billy Bishop Airport runway, avoid ferries and other random water vessels. We also had the welcome distraction of the air show happening in the city so lots to look at!