As I just posted in another thread, this website is a good starting point... search for yorkies in Ontario.
http://www.dogsincanada.com/Default.aspx?tabid=66
Several great breeders advertise there, but that doesn't mean that everyone advertising there is a great breeder.
As for what to look for in a breeder, I would ask that elsewhere on this site and I'm sure you'll get some great repsonses (more than you'll get in the Canada forum).