Is it illegal to drop gospel tract in mailboxes in Canada?

A quick call to your local post office would get you the correct answer.

It may not be illegal, but it would probably be a waste of your time and paper. Do you really think you're going to find the mailbox of a person who hasn't ever been informed (preached at) or endured proselytizing from some version of your faith?

Surely there would be something you could focus your energies on that would be more beneficial to others in the long run, preferably to those who actually seek help through God, the Bible, and the church.

My guess is you still have to actually mail them. In the U.S. you can mail unsolicited mail to people. You just have to actually pay the postage. That is what the post office gets upset about when you just put stuff in the mailbox. You never paid for it.

It's not illegal but if I were you I would wear a bullet proof vest. some of us are armed.