It might not be 100% legal, but it is as close as it can be. Consider:
- There is an exception in public nudity laws for organized events such as World Nude Bike Ride and Pride. This qualifies.
- Officers can not lay charges for public nudity without permission from the attorney general, which means they are not going to if they can possibly avoid it.
- Most experts agree that Ontario's nudity laws would not withstand a constitutional challenge based on the fact that nudity is not harmful. There was a case recently of a guy who was hiking nude in Orillia, he was acquitted, because it was not harmful.
At this point, I think you could go to the beach, or a park, or join a demonstration, and be nude, and have no fear of arrest, as long as you did not do anything else illegal.