Your stops depend on how long you want to wait before stopping to break things up. The Columbia Gorge Discovery Center & Museum is a nice stop after driving for 1 and 1/2 hours. In Pendelton, Oregon, the half way point, Hamley Steakhouse & Saloon is worth a stop. In Baker City, Geiser Grand Hotel is worth a stop as it's a hotel that dates back to the late 1800s.
Multnomah Falls by far is a stop to see. I believe you may be able to tour the falls but with Covid and weather depending, I am not positive. some great places in Boise to eat: Saint Lawrence Gridiron; by far THE BEST restaurant in Boise. I miss it regularly as I've relocated to the Midwest. The drinks are also great. Goldy's Breakfast Bistro is an oldie but a goodie. The Egg Factory is easier to get into and as good. Moon's Kitchen Cafe.
Patty