We don't seem to get very many Canadian professionals participating in the forum, so you may have a bit of a wait to find someone who can really speak to your question. (Keep checking, though.)
Meanwhile, if you haven't already done this, you might try some basic old-fashioned informational networking among people working in trademarks in your area. Are any agents listed in the phone book whom you could call, see if they would mind speaking with you about how they got started? If you can get a list of people working in the trademark office -- perhaps a staff listing on the internet -- you could see if someone working in trademarks there would mind spending a few minutes with you on the phone to chat about trademark agents to see if they know any agents they could recommend you speak with, have any insights of their own, etc. That sort of thing. Similar informational calls to attorneys in (other) law firms that handle trademarks might also get you some leads -- make it clear that you're not trying to see if their firm would hire you as an agent, but to see if they know any agents whom they could recommend you speak with about the business. You could also check and see if there's any Canadian organization of professional trademark agents and contact them.
And while this could be a long shot, there's always the alumni route--if your university has a directory of alumni which mentions what people do--you might find someone working in trademarks.
Good luck.