Ditto on going up the Alaska Highway and down the Cassiar. More wildlife visible in the Spring on the Alaska Highway than in the fall. The Northern part of the Cassiar is the worst road, get it out of the way first.
Liard Springs in itself is worth driving the Highway! Especially pretty in the Spring if there is still snow on the ground around the spring! Salmon Glacier outside Hyder makes driving the Cassiar worth the trip.
As for the trucks, when we made the drive in 2014 trucks were not a problem on either highway. Just pull over and let them pass. They will be going at a higher rate of speed than you will feel comfortable driving!
Suggest you purchase a Milepost and read about both routes. I think you will find a lot of things to see and do.