Traveling from Glacier National Park to Dawson Creek, BC

Clearances
Road conditions
You could go up 22 instead of 2 and miss Calgary. It is a nice 2 lane, wanders a bit towards the north end but a nice drive particularly mid week. May get busy week ends.
If you are going late enough you could cut west from Longview to 40 (even nicer). That is always seasonally closed but also damaged due to flood last year.

Last year we made the trip and travelled going or coming back most of the highways you're taking with the exception of 2 between Glacier and Fort Macleod.
Our trailer is 12 ft 8 in and we didn't see anything we were concerned about.
Enjoy your trip it really is awesome. On our tour we didn't encounter any really bad roads until we got to the Yukon.

If Guy and Vicki are your wagon masters, tell them Milt, Sue, Bandit, and Snickers said HI.
Milt

In Alberta they haul loads as high as 24' so I don't know where you got that information, most overhead bridges will be over 13.6' for normal truck traffic.

I agree with trigley. Not much to see from Glacier to Calgary on Hwy 2. 22 is much nicer. I suggest taking 17 through Chief Mountain and to Waterton and Pincher Creek. Head north from there on Hwy 3 for a spurt and then hook up with Hwy 22. Turn left on the Trans Canada just west of Calgary and enjoy the view. Have fun!! And I wouldn't worry about any height restrictions. Just a note that it can get a little windy in them parts so just be aware. Check out Denise's Bistro in Pincher Creek if you get the chance.

You could take #2 to Cardston, go through the town and turn west(left) on #5, which takes you past the Waterton National Park entrance. If you don't want to stop there continue on and you will be on #6 which takes you up to Pincher Creek. Go through, the sort of outskirts, of Pincher Creek to #3, turn west and go to #22(Cowboy Highway) and turn north(right). As mentioned you can go up to Longview and turn west(left) and catch 40 or keep going and go through Black Diamond up to 22x turn west(left). You will continue on through Bragg Creek to #1 which will take you to Banff etc. I don't know why you would want to go up to Calgary and then to Banff that way. It's almost like doubling back east and then north and then west. The way I mentioned, as others, is a good highway and you travel through the foothills on 22. I have taken that route many times although I cross the border at Sweetgrass/Coutts. You can go straight up 15 to Sweetgrass/Coutts unless you plan to stop in Glacier. If you go through Coutts then you would go up #4 to 501 which is just a couple of miles up the highway out of Coutts. Go west(left) and take it all the way to #2 and go north(right) to Cardston. Stay in the left hand lane to turn onto 501. Any of these routes have great scenery and as I said the highways are very good. 501 is pretty barren of houses/ranches but nice all the same. Fill up with gas in Coutts or Sweetgrass. Sweetgrass has a duty free shop. As for height I am 13ft 6 and have never ever had a problem in Alberta. North of Edmonton watch out for clearances, as I haven't been that far. This is a tad long but every bit helps. Stay safe and have a great trip. We're heading to Alberta in June ourselves.

We have also traveled most of the roads that have been mentioned by others. Highly recommend a detour to Waterton Lakes NP if you have time. We used 22 last summer on our way home from Alaska, Jasper, and Banff. We also used 40 through Grande Cache and stayed at the city campground there.

Lots of curves on the north end of 22 and a fair number of hills (rolling terrain) in the middle and southern sections. But good 2-lane road and saves a lot of miles over 2, although 2 is 4-lane.

Any thoughts on taking route 93 out of West Glacier up to Lake Louise and then up?

US 93 doesn't go through West Glacier. If you are going to pick it up at Kalispell, MT, then go north to Radium Hot Springs, BC, the 2-lane road is mostly in a river valley and is fairly easy driving. From Radium Hot Springs to Lake Louise, AB, you cross a couple of passes, if I remember right. Lots of small towns between Kalispell and Radium Hot Springs, but very few north of there when you get into first Kootenay, then Banff, National Parks. Radium Hot Springs is a major tourist area and the roads there are packed with cars and RVs in the summer.

We stayed a Johnston Canyon (near the intersection of 93 and 1) on a trip a few years ago and at Lake Louise last summer on our way home from Alaska. Lake Louise has electrical hookups, Johnston Canyon doesn't.