Well if you are taking the bus from Whitehorse to Dawson, I cannot recommend what "not to miss" along that route as you will have no choice over where you stop, if you are on the bus......
Why not rent a car in Whitehorse so you will have more flexibility both on the way to Dawson and even around Dawson itself ???......The entire town is full of historical buildings and several nice museums......there is also a really neat gold dredge out near the end of the dirt road from Bonanza that you would need a car to get to........
How much time will you have and who are we ???
If you have enough time (10 plus days) I would recommend a circle driving route to include Whitehorse to Dawson to Chicken to Beaver Creek to Haines Junction to Haines, Alaska ferry to Skagway return to Whitehorse......
Get a map, do a little research on-line in each town as to what is available and return to the forum with specific questions.....you will get a lot of helpful suggestions and opinions from locals and travelers....