As others have said, this is a tall order. Not everyone likes the same scenery, the same roads or the same points of interest. I lived most of my live in WA and have traveled extensively in the PNW and could probably answer most specific questions.
Agree with the comment about the Columbia River Gorge. There is no advantage to taking the WA side of the river. The Oregon state parks are better and I-84 is not only a well-maintained freeway with relatively little traffic outside of the Portland area but it's very scenic, as well. I would avoid I-5 north of Olympia. In fact, avoid Olympia, too. Catch US 12 to Mt. Rainier and Mt. St. Helens.
Oregon I-5 south of Portland is very user-friendly but the coast is a must see and US 101, while slow, especially from spring to fall, is worth the drive.
The best parts of Idaho are north, IMO, but if you're taking 1-84
through it, you might like Three Islands Crossing SP, near Glenns Ferry. A historic and very pretty park with ample camping.