Actually there are quite a lot agencies in GTA. The better way to find them is to check the yellowpage, the internet, the library, and HRDC. Different agency has developed expertise and networks in different field, therefore you'd better make sure which industry the agent is good at before you send them your resume.

Here are some big agencies,

www.hunt.ca
www.kellyservices.ca
www.drakeintl.ca

AppleOne
Pinstripe
CNC Global
Keith Bagg