I lived in Banff and still kind of do
I think one of the best places is Barpa Bills for a classier meal Renzo's in Canmore Coyote's in Banff and Craigs way station is still popular in Canmore. Barpa Bill is by far the best poutine in the Bow Valley.
I haven't had the poutine at Barpa Bills, but La Belle Patate in Canmore is just about the only poutine I have had west of the Great Lakes that comes close to what I grew up with in Montreal. They serve all-dressed steamies and Mae West as well.
La Belle Patate
102 Boulder Crescent, Bay 4, Canmore, AB T1W 1L2, CA
Barpa Bill's Souvlaki
223 Bear St, Banff, AB T1L 1C2, CA
Craigs' Way Station
1727 Mountain Avenue, Canmore, AB T1W 2W1, CA