Yeah, I once heard that Bell and Telus are very hesitant about activating phones that were not purchased from them. With CDMA phones you should probably get them from the company that you're going to do business with (Bell, Telus, Bell Solo, Virgin, President's Choice, Koodo). Either way, with CDMA you are going to have to go to the Bell/Telus/Koodo/Virgin store and get a phone activated if you didn't buy it from them.
I'm sure the companies that use GSM would prefer you buy the phones from them as well, but GSM technology has SIM cards that allow you to switch your number from phone to phone depending on your mood.