Bluffers' Park and Marina Quay West at the foot of Spadina, plus Port Credit Yacht Club. Since the destruction of the Lakeshore power plant, however, the PCYC has become less appealing as there isn't a permanent flow of warm water in the basin.
In other words, you'll need bubblers and 2 x 4s on hose-covered chains to fend off the occasional ice. Most people enclose their decks in a wood-frame plastic greenhouse, which means you've got a crack at keeping the heat in. You've got to do a number of things with vents and fans to keep the condensation down, however, and it's best to talk with people who've actually learned the hard way.
I would estimate that perhaps 200 people do this in Toronto each winter. It's not as popular as it once was, because people aren't as hardy, or frankly, as young as they once were as boat owners.
I'm doing it next winter for the first time. I expect to run space heaters and a diesel heater 24/7 at certain points.