It's 256 miles (412km) from Fort MacLeod to Missoula so there is a supercharger connection between Alberta and Montana and the rest of the US... at least there is in summer.
FWIW I just did this route in my 90D which now only has a max charge of 282 rated miles. As a precaution, I stayed at the Red Lion in Kalispell which has both a HPWC and a 40amp L2 Clipper Creek. I called ahead and they coned off both spots for me, but they did say it was first come, first serve for EVs of course. Anyways, I drove fairly fast 5mph over the speed limit from Fort MacLeod to St. Mary and then probably 15mph over the speed limit through Glacier NP (it was dark by then and there was almost no traffic. Saw like 4 cars the whole way and never did see a pedestrian or large animal.). There is no charge to drive through Glacier after dark, or after whenever the booth closes (probably 5pm or so).
When I arrived in Kalispell I had the same number of rated miles remaining as I had left to get to the Missoula supercharger. So driving fast had burned through my 20 rated mile buffer. That being said, if something had fallen through with the charging at Kalispell, I'm confident I could have easily made it to Missoula. Would have just driven slower of course. Also, even if the chargers were taken, there were some 120V outlets at the Red Lion listed on Plugshare, which would have more than sufficed to get me enough range over night.
Lastly, if you are just passing through and don't wish to stay the night in Kalispell, the two chargers offered by the Red Lion are pretty well set up to just top off for an hour or two to get enough range to move on with your trip. They both get 30-50mph in charge and there is a Starbucks in the same parking lot where you can hang out. There's also some other stuff within walking distance. I'm not sure if they like non-guests using the chargers, but I don't think they get much use and they are in the open parking lot on the side of the building so it might be a case of it being easier to ask forgiveness than permission lol. I think the biggest concern if you showed up without calling ahead is that the chargers would be ICEd, but even then they both have long cables, so as long as you can park within about 3-4 parking spots of the chargers, you would be fine.