Ditto on the Cascades Hwy tgo Winthrop, then turn SE thru Methow valley to Hwy 97.. this a canyon near Yakima that is a nice ride.
Get to Lewiston Id, in daytime, you will want to take pics, then head east about 20 miles then head south (might be 95 or Hwy395) ,towards a place called Riggins, nice ride, from there head to I think Old Meadows, there you can take 2 ways to Boise, I think the east route is nice. Bonneville is a prettycool place