US 2 from Spokane to near Seattle

When we come west on 2, we cut south at Bonners Ferry on 95, intersect I90 then just west of Spokane we pick up 2 again. thru Airline Heights, ( the speed trap) saves a lot of two lane highway and down town Spokane. (2 goes thru the city) when you reach Wenatchee, just west of there is the intersection to 97 south, thru Blewit pass and the way to reach I-90 again, and west to the I-5 corridor.

Your headline and write-up make it sound like you plan to take US2 all the way. If that is your objective do not take I-90 across the State as a couple of folks have suggested. Contrary to other's opinions, US2 is one of my favorite routes east to west across Washington. Goes through small towns and farm country. It's a beautiful drive, especially as you get closer to the mountains. I-90 does too, but then it's an Interstate and you won't experience the countryside.

US2 is 2 lane most of the way. Timing west of the Cascades is everything: avoid coming west from the Gold Bar to Everett on Sunday afternoon and during weekday rush hours (approx 2-6pm). Once you hit Everett and get on I-5 south you're on your own. Never know what you'll get: could be smooth or it could be a parking lot.

Joint Base Lewis /McChord.....

Make sure you know which gate to use and hours. Or go thru main gate when "truck" gate is closed. However main gate is a challenging obstacle course.

US 2 is a good route across Washington. It does not go over Snoqualmie but goes over Stevens Pass.
If you have enough time come over US 2, swing a little north and stop at Grand Coulee Dam.
US 2 goes through a town called Leavenworth. It has a Bavarian motif.
US 2 connects with I-5 in Everett, WA.
Yes, you could pick up I-90 and go across Snoqualmie Pass and then turn Southwest on WA 18 that comes in near Federal Way. It does cut off some of the heavy congestion in Seattle.
Either route is very doable with your rig.

We drove from Spokane to Washington on I-90 last summer. Yes, many miles of boring grassland, unless that's what you like. Don't know about hwy 2, but I-90 gets very windy at times. FWs have apparently been blown over and even semi trucks pull over when the wind is strong. We felt like we were driving on marbles and could only do 45-50 mph with our 29' TT and was white-knuckle driving. If it happens to be windy, I'd slow right down and maybe even stop for a while. Maybe the winds typically pick up mid-day and die down in the evenings in eastern Wa.?

A haboob rolled through the Spokane area while we were at a CG. It was rather unnerving to see the sky suddenly darken in the daytime. Fortunately didn't come near the CG.

Bit of construction in the Idaho mountains, No big deal. Other than that, being bored to tears from Spokane to the cascades. You may find it nice, but as a local, we find that drive pretty boring. Also lot's of construction on Snoqualmie pass weekdays, may hit a few delays.

Try to avoid Sunday afternoons west bound on Snoqualmie pass, as folks
heading home after the weekend, can make for some heavy traffic

Was through that way last month