That’s actually a really good question. And to be honest, I’m not entirely sure. Here’s what the government has to say on the matter:

Once your completed application has been approved, your name will be added to the International Register of Electors. When a federal general election, a by-election or a referendum is called, Elections Canada will automatically mail you a special ballot voting kit if you are an eligible voter.

That’s it. Nothing really beyond that other than who is eligible or no.