There is only one full "Ironman" event in Canada and it's in Penticton, BC every August. It's a 3.8km swim, 180 km bike, 42.2 km run. There are a few other ironman-distance events in Canada, but that is the only Ironman-branded event.
There are a number of different triathlon events though. Lots of half-ironman events around (called a half or a 70.3) including a two pretty big ones in Peterborough and Muskoka. After that there are the Olympic or Standard distance triathlons ; 1500m swim, 40k bike, 10k run, and a sprint distance is 750m swim, 20k bike, 5k run. Sprints can be done either in a pool or open water.
Lots of different levels and distances to choose from. I've been doing triathlons for a few years and Olympic distance is where I focus my time. Personally, I would like to enjoy and focus on the shorter events, tune up my race strategies and then look at the longer races once I feel like I'm dialed in. I am very against those folks that choose an ironman as their first triathlon...it happens, but I can't see how it would be an enjoyable experience... ok ranting a bit here.
Anyway, change it up, do some intervals and I can't say enough about shorter TT's...lung-burning, balls-out riding is lots of fun.