Winter golf in Seattle/Marysville? Think drainage!!
On the public side in Marysville you have 3 choices: Kayak Point, Battle Creek and Cedarcrest. Kayak Point is the best of the 3, but it is very soggy during the winter months.
Next closest would be Legion Memorial in Everett, a pretty good muni that underwent some major renovations in the past decade and drainage is much improved.
Continueing south you have Walter Hall and Jordan Wall's favorite course Harbour Pointe. Harbour doesn't drain particularly well and is fairly pricey, it has some good holes, but housing has seriously encroached on the course.
If you go north I would recommend Eaglemont in Mt. Vernon, a tough but interesting course, with fairly good drainage.
Further north there are a number of interesting courses, Avalon, Homestead, Semiahmoo, North Bellingham and Loomis Trail.
Can't help you with the private side up north because I haven't played any of them.