Hi There,
Unfortunately, I'm not from the GTA, so I can't give you any vet names specifically, but I can give you some advice as how to look for one. When I found my vet in Waterloo for my girls (away at school), I started out looking under vets in the yellow pages. Next I looked at the ones which were advertising specifically for exotics and called around asking about their experience with guinea pigs. I ended up with a great vet who had special certification with the vet college and specialized in exotics.
Also, I would do some looking around the net at care pages
http://guinealynx.info/ is a good site to start out with. That way you can go into the vet with a good idea of what is going on, and what to expect. Also, I would message the symtoms on one of the boards so that some of the more experienced pigger persons can try to help out.
Good luck in your vet search, and hope the little one gets well soon.
Jess