Well
Fido is being bought by Rogers as of November 2004.
Basically, there's only 1 GSM network in Canada. It operates 850 and 1900.
Like you've said, Nokia 7270 is a tri-band phone with 900/1800/1900. So the phone will work, but not as good as a phone with 850mhz.
But it shouldn't be A BIG problem, but I will always suggest a phone with 850mhz to use in North America.
kalok~