Release the lawyers ...
Honestly, I have no clue if my case would be legit at all, though I do have the original Photoshop files on file, and the fact that the shirt image and mine ARE THE EXACT SAME. I can even point out the parts where I fucked up. But as you can see, this was made before I started putting copyright stamps on my digital images. Plus, he's in a different country. WHAT CAN I DO TO MAKE THIS BITCH BLEED?!?!?!?!
Luckily for you, and all other artists out there including myself, you don't have to put copyright stamps on your stuff in order for it to be copyrighted. According to current laws, unless you go on record stating that your work is public domain, it is automatically understood that said property is owned by you and under copyright. Now the fact that he is in Canada might be a problem. However, I'm fairly sure the Canadians have laws similar to our own regarding this so there might very well be avenues of legal recourse you can pursue.
Whilst that is quite true, if he can't prove he created the image then he won't be able to sue for copyright infringement.
I'm no expert to be sure, but I don't think photoshop files are gonna cut it. You need to be able to verify the date you created the artwork and then let him attempt to prove he created it beforehand. Creation dates on a computer file can easily be faked.
I was always told to seal things in an envelope and then get the post office to date stamp it and post it to yourself, and then leave it sealed obviously.