It depends on what you want to learn.
No, really, it does.
I think Rescue is a class all divers should take. Not only do you learn some useful things about how best to approach and aid a person in distress, you also think a lot about how they got there and how you can avoid joining them. Rescue does not require advanced diving skills (more just watermanship) so it can be done at any time.
It is my own personal opinion that the vast majority of divers would benefit from learning better buoyancy and trim control, and some non-silting kicks. Some Peak Performance Buoyancy classes are very good, and some are not. No mainstream class I know of below cavern teaches non-silting kicks as a routine part of the curriculum.
Learning more about decompression and what the tables and computers are telling you is very useful information as well, as is learning some gas management. Neither is contained in any standard class that I'm aware of (except for individual instructors who will add such things on their own).
But given that you are in Ontario, you have access to a superb class, which is GUE's Fundamentals. Dan Mackay, one of their instructors, is based in Ontario. You might do a search on some Fundies class reports, and see if this sounds like anything you'd be interested in doing. It does require some equipment changes, at least for the duration of the class, but a lot of the information is usable no matter what configuration you decide to go with after the class.