Heights will be the least of your problems on that route. Potholes, construction delays, slow traffic jamming up the road, and gravel flying up and striking your rig face exceed any heights. I don't remember that much incline or altitude to it, until you get around the Stone Mountain area.

When you are talking about traveling to Dawson Creek to pick up the AlCan, I presume that you are talking about driving up from the south and east to DC, from Idaho or MT.

If I were doing it, I'd probably drive to Smithers BC and west and north to pick up the Cassiar Hwy. You can always drive up one route and come back the other. By early September, most construction on the roads is done and you can make better time, but by that time, the winter has almost set in. The earlier in the year one travels up there, the less construction is complete.