Capsizing and Self-rescue
Capsize and recovery is an important thing to practise. It is very difficult to swim when clothed, especially if you are wearing additional camping gear like heavy boots and bags. It's even harder to swim if you start off with the surprise of your canoe tipping over and the cold shock of freezing spring water swallowing you up. If you don't prepare for and practise this, it could kill you. It's not rare that you'll hear of this happening to someone on a lake you're visiting, be prepared!
All I can do here is share in brief that steps that should be taken, but this is something you should practise with an experienced instructor.
As soon as your canoe tips, keep it from becoming fully submerged or else it may sink. You can do this by tilting it so a pocket of air can be trapped inside of it, like a toy you'd play with in the bath. You can leave the canoe up the right way with water in it for a bit while you get yourself in order, but you really should be getting back in there as soon as possible. The last time I flipped my canoe, I left it with water it in upright so I could grab my hat and adjust my PFD to stop riding up around my neck.
Ideally you have two people to help with the next step. Get the canoe wrong-side down supported by your hands. Quickly flip the canoe over, trying to not capture too much water while doing so. You should have a bailer, so even if you don't do a great job of this you can bail out the excess water. You'll find it difficult to flip the canoe like this without a firm base to push off of (swimming), it takes practise.
Once the canoe is flipped without too much water in it, you and your partner will take turns getting in the canoe from the front or rear of the canoe. You can't climb over the side, because it'll tip again. You have to climb from the front or rear carefully, hopefully with a friend holding the canoe steady.
If you're in a canoe but others are not, it's not trivial to get them in without tipping the canoe. In Canada, all canoes have to be equipped with throw bags which you tie to the boat. You can throw this bag out to the floundering person so that they can reel themselves in.
You can also use your own canoe to help flip a tipped canoe by pulling it up across your canoe faced-down and then tilting it into the water right-side-up. This is another thing that has to be practised in safe conditions - you could easily end up with two flipped canoes!