Actually drive Hwy 542 to Picture Lake is priority over

I-90 on your July trip. It is a relatively easy side trip on your way back from/to Canada off interstate 5.

I-90 passes by Snoqualmie Falls, which Erdong had a picture of. But it also takes you over Snoqualmie Pass, highest point on I-90 crossing the Cascade Mountains. The east slopes have drier and different landscape vegetation. Too many west - east bound routes to choose from, hwy 2, hwy 20, and I-90. They are similar in a sense and I would try to do them all in one trip. It's quite a few loops.