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If you go in October, make sure it is before Canadian Thanksgiving, October 13. I believe after that date is when most things will be closing.
Snow can happen at anytime of the year there. I've been golfing in Banff in July and had sun, rain, sleet, and snow all in the space of 6 holes!
Been there in October and had 75F temps, another year in October brought temps of -10F temps. The average is 50F during the day and below freezing at night, but for the most part it is usually sunny.
It's a good time to go, no crowds. You can find that you have some places to yourself.
Make sure you get yourself to Lake Louise early in the morning when the lake is still, absolutely stunning.
Have a look at these eBooks: http://www.darwinwiggett.com/ebooks/
You may find them useful.