They built the Alcan highway between Fort Nelson and Watson Lake in some lowish mountains rather than following a lower route along a river. A lot of pilots fly the lower route if it's low ceilings. It is north of the Alcan and follows a river.
There is another highway, the Cassiar highway to the west, aka Highway 37. Depends on the weather. Sometimes it is clear when the Alcan is cloudy. It joins the Alcan at Teslin, near Whitehorse so you still can fly the Alcan to Alaska, which is a nice part. Very far north feel and remote.
The prevailing winds are south to north up the coast and west to east down the Alcan, so seasoned travelers trying to fly the wind frequently go up the coast and down the Alcan.
There is an argument, for history's sake, up the Alcan and down the coast is the way to go and that is what I did the first time (actually went up the Cassiar because of better weather there, but its about the same). I went up the coast and down the Alcan the second time and it was quicker. The coast is RAINY and remote and over water.
You have to pass customs and there is mandatory flight plans in Canada, but its about the same as flying in the USA. They tend not to have courtesy cars at their airports. But I never had a hard time finding a hotel and camping at the smaller airports was allowed.
Best week for clear weather is first week in July. I went the first time in August and had a lot of rain. I went in first week of July second time and the weather was better. Still, I had some rough weather both times (July was substantially better). You are just about bound to hit a storm no matter how you do it and have to wait it out and/or divert.