Currently there're 5 major cell phone companies: Bell, Rogers AT&T (Cantel), Tellus, Fido, Clearnet.
From the ads, we got to know that it's almost impossible to purchase the service without buying a handset from the same company. Each company uses only certain models and certain brands of handset, and they do not provide SIM-card-only service. For example, Nokia 5190 is only sold by Fido, other companies sell different models of Nokia, but not 5190. Errison T18Z is sold by both Fido and Cantel, but both of them don't provide handset-trade-in service.
In this case, I don't think bringing a handset from China is useful.
BTW, the cheapest handset here is $50, usually you can buy a satified one from $100 to $225. If you convert these prices into RMB, you will find they're quite cheap. As a result, I suggest you to sell your handset in China, buy a brand new one after you come to Canada.