I visited the Canadian Rockies in Parks Canada three consecutive years only in September (2011 thru 2013).
For the exact days the OP is planning to be present, do check which campgrounds with electric hookups will still be open as Parks Canada will start phasing in upon seasonal closing of some campgrounds during September.
As noted, I can also contest that you will need reservations (only if you want electric hookups) at Whistlers in Jasper National Park as I only dry camped there and at the Icefields the whole times I was in the Jasper area.
Lake Louise, Tunnel Mountain I and II, (and the non lake campground side of Two Jack Lake while still open) during September have spots generally available with no reservations in Banff National Park....
I never had a problem getting electric hookups at Lake Louise with no reservations - (the layout is super friendly for big motorcoaches)... you might want earplugs if you are sensitive to fast noisy trains flying by.
Tunnel Mountain I or II could be a crapshoot for electric hookups with no reservations -
I never had a problem getting a dry spot at Whistlers.
Other than Lake Louise Campground, I would suggest reservations if one wants electric hookups during September (after holiday weekend).
Those were the only six overnighting areas I had stayed at in Banff and Jasper National Park upon my visits.
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