Yes, Hwy 20 is the way to go. Hopefully the fires will be contained by the time you roll through Okanogan. I've been working in the Methow valley for a few weeks, and some days the smoke was really bad. i would stay very far away from HWY 2, not only because of traffic, but the air around Wenatchee is currently considered hazardous, and they are telling people to stay indoors.

Enjoy HWY 20, it is absolutely stunning.

Air quality map:
https://fortress.wa.gov/ecy/enviwa/Default.htm