Sorry if the actual law bothers you. If you felt that his actions were defamatory, you would contact the owners of GFY.com to have it removed. If it wasn't removed, you'd send a C & D. Then you would go after them. The defamatory content is on their site and their servers. This has been established in many cases already in the US.
However, even if you could sue SOS for the damages and GFY was not liable for their own site, you would need GFY to provide proof it was him that posted. This would require IP checks, etc. I would have your lawyer do that first before filing a suit as any court in the country is going to ask you to prove he posted it.
You also have to prove that damages occured by the statements that were made. According to YOU, they didn't:
https://gfy.com/9592200-post13.html
Unless something has changed in the past 3 and a half weeks, you'd have a hard time explaining that.
Finally, the copyright issue is again with GFY, not SOS. I'd advice you to point your lawyer in the direction of the recent rulings between Perfect 10 and Google.
However, maybe Canadian law is totally different. But unless your suit completely spits in the face of past legal precedent, you'll be laughed out of court (and most lawyer's offices).