The route you've outlined (at least up to Stewart) is actually good paved road. Past that, I have no experience. West of PG to the hwy 37 turnoff at Kitwanga is in quite good condition and smooth as of August 2012. It's been a lot of years since I've continued on up to Stewart, but the last time, the pavement was good, as well.
Once across the Alaska border to Hyder, all the streets are dirt/gravel, but it is also really small. If one wishes to drive on up to Salmon Glacier, the road continues with a more or less decent gravel surface.
Also, once in Hyder, be sure to pick up a bottle of Clear Springs grain alcohol. It's 190 proof (95%), and you won't find it anywhere in Canada, or perhaps even most places in the US. This is the stuff they use for the "Hyderization" ritual.
Another thing to keep in mind is that once you're off highway 16, and realistically just a few miles past Smithers, there's no cellular coverage until you're up in Whitehorse. I don't know if the VHF radiotelephone network is still operational, but that was the only way we could communicate to the phone network back in the day. Now, satellite phones would work, but who uses those...? If anyone has a hand held HAM unit, I suggest bringing it.