In reply to CacCarnBeag:
I've used Rentfaster.ca, but that seems to be long term rentals. Apart from Kijijiji, as you mention, you can put a message on the following FB groups: Rockies Ice and Mixed Conditions, Calgary Climbing Community, Calgary Area Climbers, Bow Valley Climbing Community, Canadian Rockies Ice Climbing.
The rental market is really tight and you'll be in competition with the seasonal workers who can't find, or aren't provided with, accommodation in Banff.