Anyway, trying to reply and will give it another whirl.
A little beauty of a place to stay, that's quiet and has beautiful scenery all around, is
Baker Creek Mountain Resort on the Bow Valley Parkway. Gorgeous little individual cabins or you can stay in the lodge if you like. The Trapper's Cabin is the nicest but they're all pretty decent. If you stayed there and talked to staff ahead of time, I'm sure they'd help you set up anything you'd need or want. We stayed there for an anniversary once, and they found out and had a little bottle of champagne and some chocolates waiting for us.
Sharon Auld at Naturally Chic has helped set up proposals, so you could maybe get in touch with her and see what she might have to offer you.
If you're at Lake Louise, you could contact Brewster's ahead of time and arrange for a private horse drawn sleigh ride -
pricey though. In that same vein,
Snowy Owl sled dog tours might be another idea. Talk to them at the time of reservation and see what places they might recommend riding to, for a proposal, and what they might be able to help you set up ahead of time.
Spur Line Trail Bridge in Canmore - not sure how private it would be though.
Storm Mountain Lodge might be another option. Just off the TransCanada on the way out to Lake Louise, south on Hwy #93.
Very rustic cabins.
If you go to Johnston Canyon, get directions to
this place/the rock, along the trail, to give her
the rock. Depending on time of day, it can be busy with photogs but pretty cool.
ETA: if you want a photographer to catch the proposal, shoot me a PM. I can give you a couple of names of photogs you can contact to see if that's in the budget etc.