If you are departing from YYZ, there is a high probability your bags will be weighed and size checked - do what we do - if you're traveling solo, find a place to store your bag securely while checking in so they don't see it, and if you're traveling with someone, have the other person hide out of sight with the bags while each one of you takes turns checking in. Have a small light backpack with a few things so they see you at least have something.