I second going through Spokane. me and a few buddies make the drive every year for a Seahawks game. We've gone highway 1 (sloooooooooooow), highway 3 through osoyoos (nice drive, but long), but the best is highway 3 and then down through coeur de lane and spokane.
Spots to hit on the way:
Coleman 7-11 chicken...like the 7-11 chicken in Claresholm or a number of other small towns in Alberta....better than KFC by far.
world's largest dump truck in Sparwood...you haven't driven that road until you have a picture sitting in the wheel well of that truck
Silverwood theme park about 15 minutes north of coeur de laine, just off the highway, only open sometimes, but it looks like alot of fun when I drive by.
Spokane has a sonic drive in, as well as Carl's Jr and JITB...but the city is a S*** hole.
Ellensburg is about 2-3 hours east of Seattle and has possibly the best burger I've ever had at the Campus U Tote-em, right by the University there.
http://www.campusutotem.com/
Seattle has the ever popular Sizzler...I once ate an ice cream taco there, and a corn taco creation with meat sauce, cheese, pico de gale and jelly beans. greatest place to visit if you`re with friends.
I eat alot.