oof, the repeating integers!
washington state, or the entire cascade mountains. east or west side will do, but stay on the west side so you can easily go back to your hotel at night and not worry about snowed-up roads
the more north you go, the more extreme the views, the less reliable the roads, the less people you see, and the worse the hotels. but goddamn, if that cascade range around northern washington and southern british columbia isn't the most beautiful place on earth, I don't know what is. you might even want to head more eastward towards some of the glacier lakes, or southward, since there'll always be something to see even in the rest of the pacific northwest, but the mountains are thematic for christmas. crater lake, or the redwoods of southwestern oregon are also unforgettable and alien sights, especially if it's snowing
if you go to washington, be sure to spend at least one day climbing mount rainer, and spend at least one day in a hotel room with a window facing towards rainier. it's not that difficult to find, since the thing is tall as fuck since the surrounding lands are practically coastal. the sight is on par with mount fiji