Are you at least in a 3G coverage zone? (in this case, I'm referring to HSPA+ coverage -- not CDMA). If not, the phone won't work at all, since Telus/Bell (and their sub-brands) don't support GSM/EDGE service.
Given that on Rogers you'd only see EDGE coverage, I'm guessing that you are in a rural area. In that case, I'm sure the carriers would be more likely to use the 850MHz frequency so that it can cover longer distances with fewer towers.