In Canada as in the UK copyright is from British common law. Copyright belongs to the authour from the time of creation of the work. What you need to be able to do is prove that you created something before someone else can claim to have done so. If a letter to yourself containg a copy of the work is postal dated but remains sealed it can be taken to a court official such as a justice of the peace or a judge. He will open the letter to confirm the contents and you will take an oath that it is your creation. The burden of proof would then be on the other party to prove that they possessed the work at an earlier date.
Publishing a work certainly dates it but is not a requirement for copyright. BE VERY CAREFUL OF PUBLISHERS FINE PRINT! Many of these bastards steal copyright!