I'd suggest a minor change. US2 through the Cascades west of Leavenworth is narrow and twisty for a major highway and is heavily traveled by commercial trucks. As an alternative, I'd suggest Highway 20, which is the northernmost of the Cascade passes.
It has been greatly improved in the last 5 years or so, is a four-lane road most of the way, is much quieter (very few trucks). Assuming you're headed west on US2 out of Spokane, take highway 97 north at Orondo, then pick up 20 a little way west of Okanagan. You'll meet up with I-5 at Burlington.
I don't know how the distances compare, and I'm a bit biased towards Highway 20, as we live out at the end of 20-spur in Anacortes, about 35 miles west of Burlington.We also like it because it goes over 5200' high Washington Pass and the scenery is spectacular. It does get closed for the winter, usually late October, because of snowfall. There isn't enough traffic to justify the cost pf plowing it.
Do a bit of map reading and see if the mileage difference makes sense in your particular case.
If you have the time, I'd suggest coming out to Anacortes and spending a day on the State ferry system and seeing the San Juan islands.