You would think so, but in my experience you can usually get a prepaid with a SIM for less than just a SIM.
Your choices are Rogers, Fido (owned by Rogers but run separately), and Telus. Bell and the other wirelines are CDMA. I think you will find that the phrase "cheap Canadian prepaid" is an oxymoron, but you can poke around on their web sites and see what they have to offer.
R's, John