The only Canadian providers that operate on a GSM / GPRS network that uses SIM cards are Rogers Wireless and Fido. Fido is now owned by Rogers!. Fido is only a viable option if you plan to spend most of your time in a major city. So really, Rogers is your only option! One thing you will have to cosider is wheather your Service Provider in the UK has locked your phone so that it only works on their network no matter who puts a SIM card in there.
I went to Australia last year and intended to do the same thing but Rogers had locked the phone out from accepting any non-Rogers SIM cards. the best way to unlock your phone without paying an arm and a leg is to go to a search engine like Google and type ” unlock GSM “. you will find an outfit that can unlock your phone for about $20-$40.
However, it seems as though the general consensus of this thread is that Telus has better coverage in and around Fernie and that would require you to buy a phone from them!
Hope this helps!