Belfair is at the tip of the Hood Canal hook, right? So you'd probably cross the Narrows bridge, unless you do the ferry. So it's south Sound both ways.
In terms of traffic I worry most about east bound on US2 Friday afternoon/evening, and west bound Sunday afternoon. And mostly that's in the semi-suburban parts from Monroe, Sultan, Gold Bar.
Check WSDOT for pass conditions - should be good. There has been construction on I90 on the east side of the pass. WSDOT will have good information on whether that will cause any delays.
From Vancouver US12 to Yakima is an option, as is I84/WA14 to US97. That's scenic in its own way. And you'll still get Blewett.
In a vague sense US2 is more scenic east bound. It takes you gradually into a deeper canyon, then climbs quickly to the pass (best views to the north). Then a gentle drop to the Lake Wennatchee turn off. Then narrow Tumwater canyon, with corner and abrupt entrance to Leavenworth.