I avoid freeways like the plague. This is the way I would go. White Pass is very doable. WA 24 & 26 are good roads and basically flat and US 395 is all four lane now up to I-90. Plus is that you miss pulling the grade out of Vantage. Used to run Portland-Yakimia-Spokane and from Yakima that was the route we took.
https://www.google.com/maps/dir/Long+Beach,+WA/Spokane,+WA/@47.284874,-117.7064745,9.87z/data=!4m24!4m23!1m15!1m1!1s0x54930d412550d6c9:0x8d06ff04da86900!2m2!1d-124.0543234!2d46.3523219!3m4!1m2!1d-121.5405462!2d46.8675459!3s0x5490cba160e05085:0x212c1d70751c219f!3m4!1m2!1d-119.6894794!2d46.6661755!3s0x549852eaa81c597d:0x18f0f873b6b8c161!1m5!1m1!1s0x549e185c30bbe7e5:0xddfcc9d60b84d9b1!2m2!1d-117.4260465!2d47.6587802!3e0If you go Portland you aren't missing any grades as you need to make the pull over Horse Haven on I-82 between Umitilla and Kennewick.