[slaman]

In Canada, mail in ballots have a separate, earlier deadline.

If you do not mail your ballot on time, there is another simple solution, you go to the (lineless) polls on election day.

When they check everyone in they confirm that they have not already received a mail-in-ballot from that individual before allowing you to the booth.

With enough time allocated for mail-in-ballots, I feel that it doesn't matter that the deadline is earlier. Deadlines are fairly arbitrary either way and at some point you need to select a winner.

If you have plenty of opportunity to vote and you do not vote by the deadline, your vote is not counted regardless of the method you have chosen.