I'm no expert on the sights of NW USA, but I did a wonderful bicycle ride a few years ago from Canada to Mexico. My route crossed from Canada into Montana at Roosville, went through Missoula, Dillon, Idaho Falls and south from there.
Yoho Park in British Columbia is cycling distance (3 days if I remember, so less than a day on a motorcycle) from Roosville.
I used maps from America's Bicycle Travel Inspiration & Resource - Adventure Cycling Association
These maps are something different. Specifically for long-distance cyclists, they list everything such a traveller needs. For instance, on a bicycle it's a major disaster to take a wrong turn and continue for two hours until you realise, especially if that two hours is downhill. So these maps are detailed enough to prevent that.
They also list all the sights and features that would be of interest to a cyclist, and as far as I can see they are the same as would interest a motorcyclist (I'm one, doing more motorcycling than cycling). They also avoid freeways, generally.
So I'd recommend these maps to anyone wanting to explore the 'quieter' parts of the US.
You need to note though that quite a few of these maps cover off-road cycling routes that maybe aren't open to motorised traffic. My journey was entirely on roads for motor traffic, but not all tarred. These maps show the surface nature of any un-tarred roads.