WA20 crosses a ridge between Colville and Tiger (junction with WA31). I've been at both ends, but never crossed it (instead using a higher paved Forest Service road between Usk and Chewelah). It's not listed on WSDOT's list of passes. On Google Maps terrain view it looks like the climb from the west is gradual, with a shorter drop on the east side, about a 1000 ft with a few loops.
The rest of 20 follows a river.
Going around to the south (395 to 2 with some sort of cutoff) should be a bit lower, but also more 'urban'.
How are you getting to Kettle Falls? US395 from Canada? From US97, Sherman Pass (between Republic and KF) is higher, in fact it is the highest of the WSDOT passes. Not that anyone has complained about grades, curves or drop offs. I'd put it in the same category as Kootenay Pass (BC3) which I suspect you are trying to bypass.
