I mean, it's not really optional for Canadians _not_ to sign up for the list. It's the official list of electors. If you're a citizen, you're going to end up on the voter list one way or another.
Technically true, but you can register at the polling booth on the day of the election, and there's a checkbox that lets you opt out of saving your data in the database. [0]
There are many reasons an individual may choose to not be on the list (eg. domestic abuse situations).