Ignore Johnston Canyon it's not very interesting to walk and is packed with all sorts of humanity. You're better to hike around Lake Louise which while equally busy is the postcard picture they should all take. Hike up to The Beehive and teahouse. You should go to Maligne Lake and if the bears aren't active hike up to Constellation Lake. It's reasonable easy. Grassi lakes outside Canmore is also a simple hike. Another option is to go up to the base at Sunshine and do some hikes from there.
Troll Falls in K Country is also pretty relaxing for a warm up or cool down day.
Only warning I'd have is check in with the rangers to see the bear activity or check online.
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