For Bellingham, I90 to I405 to I5 makes sense, especially if you can avoid rushhour traffic. There are alternatives across the Cascades that bypass more of Seattle, but they aren't freeway.
It's easy to cross from I90 to US2 around Quincy. At the west end, US2 meets I5 in Everett, still within the greater metro area. Disregarding traffic issues, US2 probably adds an hour to the drive.
WA20 is a more scenic route, meeting I5 just north of the new bridge. But it probably adds a half day to drive (compared to I90).
Looks like Alaska boats leave Bellingham Friday and Saturday at 6pm.
If I were making that trip, I'd aim to camp at the Columbia River (Wanapum State Park). With a 2hr drive to I405 that would put me in the Seattle metro area midday, with plenty of time to get to Bellingham by early to mid afternoon.
