By ALL means do the Cassiar and visit Hyder. The boardwalk along the river provides great bear viewing. A few miles above the viewing walkway is Salmon Glacier, which you look down at. Both are quite unique, and you'll have the opportunity to pass through Banff, which is equally picturesque to much of Alaska. I also enjoyed my stop in Houston, ?BC?
As for road conditions along the Cassiar, you shouldn't find it any rougher than the worst you've been on during your trip. You may want to venture into Watson Lake to fill fuel tanks. The station at the Junction tends to be considerably higher per liter. That'll also give you another chance to stop at the signpost forest.
Have fun !!