According to previous discussions (search for N900 in Canada - Toronto), the Bellus network will not work for data on the N900. Bell/Telus are still using 850/1900 frequencies, and their networks are apparently 3G only, so they won't drop back to EDGE 2.5G data. That means you can only use the N900 as a regular GSM phone on their networks, not for any data. The iPhone uses the 850/1900 bands for 3G, which is why it works.

I don't think that Bell, Telus, or Rogers has made any use of their newly purchased AWS spectrum, so for the moment, your only choice for data is 2.5G EDGE on Rogers/Fido.