You should put more information about what you're asking.
There are many differences between the 3 Canadian carriers, some bad, some good.
You don't tell us what kind of phone you're interested in getting and for what.
Rogers, as of now, is the only GSM/3G/UMTS carrier in Canada (Fido is Rogers, remember) while Bell and Telus are still CDMA carriers (although both are planning to roll out their respective 3G/UMTS networks).
Rogers is definitely the most expensive carrier to go with although it's the one with the best phone choice.
Bell has good plans, specially for Blackberry.
Telus, I simply don't like. Bad network reception, too many call drops, too many times you can't even place a call because its network is overloaded.