Route to Banff from Montana

I would go up through MT on US 89. Spend the night around St Maries, MT which is east entrance to Glacier NP, cross into Canada and visit Waterton Lake CAN NP.
Continue north toward Fort MacLeod.

Thanks, Bud, in fact I'm coming back exactly that way, but I am really planning on staying at Conestoga Campground near White Sulphur Springs and prefer a route just east of the one I'm using on the return trip. I'm grateful for any suggestions and appreciate your response.

East of there would be I-15 that changes to CAN 4. Couple good campgrounds around Lethbridge, ALB

There's also Gold Springs and Milk River campgrounds just north of The Sweetgrass/Coutts border crossing. Milk River is a small campground and we usually stayed there for one night while on the home ward bound part of our semi annual trip out west.Tried to get into the Gold Springs campground on a Labour day weekend but it was full up. Being retired we forgot about the holiday weekend as we're on holidays permanently. Waterton National Park can't be recommended enough by us. We always stayed at the Waterton Springs Campground for a couple of weeks and it's a mile or so north of the Park gates. You could go north from there to Pincher Creek and grab #3 hwy from there west bound to Hwy 22(Cowboy Trail) and take that right up to Hwy #2(trans Canada) to Banff.Hwy 22 is in the foothills and it's a nice drive and good road.There can be heavy duty winds apparently but I guess we were lucky because we never experienced any...there.

Thanks, Pipeman. Our only other RV visit to Canada was to Ontario. We stayed at the Fifty Point Conservation Area on Lake Ontario for our first and (so far) only visit to Niagara Falls. Some Ontario RV friends met us at the campground and stayed in their RV with us there. That remains one of the favorite campgrounds in all our travels.

I have always wanted to see the Canadian Rockies, but it is a long trip for us. When we allow for reasonable driving days and a few stops along the way, there is not enough time left for the kind of visit that would be the best. We are not full-timers and a month away from home is near our limit.

Right now I am considering a campsite in Clarisholm after crossing at Sweetgrass. Are there any comments about that from anyone? Or suggestions about routes on to Banff from there?

Since you are staying at Conestoga Campground, Smith River Valley (White Sulphur Springs, MT.) Which I think is a membership CG you may think about Bridgeview RV Resort in West Lethbridge, Alberta which is C2C and AOR and RPI and is a very good (Much better than Conestoga CG) campground. From Lethbridge is a easy days drive to Banff.

Pipeman wrote:
Milk River is a small campground and we usually stayed there for one night while on the home ward bound part of our semi annual trip out west.

We stayed at Milk River because it is very convenient going south if you want to go through the border crossing early in the morning. Quite a few full-time residents and the manager was absent a lot, but it worked fine for us on our way home from Alaska (we stayed in much worse up there!). It is on the south side of town next to the golf course and the river, so you could even get in a round or go canoeing, if you are so inclined.