Early fall is a great time to fish Alberta and you should do well. The streams will be low, clear, and cool. Near Rocky the browns in the Clearwater River will be willing to play. The Raven and Stauffer are also good but quite challenging. The area of the Ram that garners all the raves is extremely difficult to access on foot. Unless you want to book a helicopter you would do well to not try. The Blackstone is easier to access but the river bed is in a high energy flood plain and the wintering holes change too much to produce numbers of cutthroat but is still fairly good. There are other streams in the area that are fun but come with their own challenges. Fishing out of Rocky you would be doing a fair amount of travel.
I believe you would do better to go south out of Calgary and fish out of the Crowsnest Pass. The area has very good fishing for Cutthroats, Rainbows, Browns, and Bulls. The Crowsnest River and Oldman River and its tribs are easily accessible and information on where and how is easily obtained in the local shops such as Crowsnest Cafe and fly shop in Coleman where you will not only get info and needed flies but also your lunch and or breakfast.