Copyright protection is automatic under Canadian and international law from the moment of creation of work, provided that the work meets these three criteria:
1) The work must be original.
2) It must be fixed in a somewhat permanent material form.
3) The author must meet the qualified person requirements set out in the Copyright Act.
Registration is not required for protection in Canada. However, the Copyright Act provides that a certificate of registration of copyright is evidence that copyright exists and that the person registered is the owner of the copyright. Having your work on the Register of Copyrights may also help those wishing to seek permission to use the work. For more information go to the Canadian Intellectual Property Office at https://www.ic.gc.ca/eic/site/cipointernet-internetopic.nsf/eng/h_wr00003.html.
Keep in mind that there is a cost associated with registering copyright, and if you decide to copyright every work you create, you may or may not receive a return on your investment.
Mailing a copy to yourself is not the same as copyright registration and is not a form of copyright registration, nor is it a reliable form of evidence of copyright ownership because there are several ways with which registered mail can be tampered with (for example, mailing yourself an unsealed envelope and entering contents at a later date).
There is no harm in mailing yourself your own work, but it will likely not be given serious consideration in the event of a legal dispute.
One thing you can do to help support a claim of copyright is saving the different versions of your work on your computer, beginning with the earliest, and maintain back up files. Of course, if the other individual has computer files with original content predating yours, you will not win a lawsuit unless you have compelling evidence of copyright infringement.