I've driven between SEA and California (usually Southern) over the winter holidays on numerous occasions.

Everything subject to short-term weather forecasts, my recommendation is to use I-5 as far as Drain, Oregon (a bit north of Roseburg) and cut over to Reedsport using Oregon Highway 38. It's a very scenic road, usually some roadside elk, and the last 20 miles or so into Reedsport are through the very scenic Umpqua River canyon.

Overnight in Bandon, one of the nicer and more scenic towns on the Oregon south/central coast. There are some okay restaurants in the Bandon "old town" near the harbor.

The coastal scenery between Bandon and the California line is about as good as it gets on the Oregon coast, so take your time, and take plenty of time going through the Redwoods south of Crescent City. All the "grove" turnoffs are excellent, even if it's misty/raining.

Try not to drive between Crescent City and Eureka at night or near "sunset." The road can be twisty and hard to track sometimes, and if nothing else you'll arrive at Eureka pretty knackered. You might give a tryout for a meal at the Samoa Cookhouse in Samoa (over the bridge from Eureka) - family style meals in a lumber camp mess hall, served by your Grannie, provided your Grannie talked like a lumberjack. Ferndale, a bit south of Eureka, also has lots of twee bed-and-breakfast places in Victorian houses. Haven't been there around Christmas, but I imagine it's the town that puked Christmas, if I had to bet.

If time permits, the stretch of California Highway 1 from Fort Bragg all the way into SF (it rejoins 101 shortly before the Golden Gate Bridge) is one of the most beautiful highways in the US. Take it if you can.

Go to http://dogfriendly.com/ and/or http://petswelcome.com/ for excellent leads on accommodations where your pooches are allowed. We usually look for dog parks with off-leash facilities as destinations for rest stops; there are quite a few in the Seattle, Portland, Salem and Eugene areas, relatively few and far between on the Oregon coast or northwestern California, but some.

Be mindful of short daylight and the almost near-certainty of rain, wind, etc. on the coast, or if you decide to go inland, snow in the Siskiyous and/or black ice in the Rogue Valley and parts of the northern Sacramento Valley. It's that time of year.