I don't know about the rules in Canada, but in the US, as I'm sure you both know, any qualified sender can apply for a Mailer's Postmark Permit and cancel their own mail with whatever design they want, within certain limitations.
Here are a couple of examples.


There is even a Mailer's Postmark Permit Club that collects such markings,
http://www.shaulisstamps.com/mppc/index.htmlIf you received your Par Escargot cover in the mail recently, why not send a postcard (or email) back to the sender to get information directly from them? I suspect the sender is the creator and origin of the cancel, it seems like too much work for someone further down the stream to create such a nice presentation.
Let us know what you find out. :-)