Last summer we arrived in Fairbanks in late June. We also traveled from Dawson Creek to Dawson City(via the Klondike) and then over to Tok. We saw and read about plenty of dump stations, but like you said, don't know if they are open that early. We did not stop at any CGs that did not have a dump station, and we stopped frequently. Also, we saw some gas stations that had dump stations as well.
The Al Can was in pretty good shape with some construction here and there...can't speak to it's condition from Whitehorse into Tok but that section is well traveled, so I suspect it's fairly well taken care of and passable. Canada and Alaska winters make everything subject to change. It IS a great trip.