Michigan to Seattle over Thanksgiving?

12/30/13 I90 Montana border with Idaho

I would go for it . Take I 80 I 84 instead of I90 a lot less mountains....just leave early and watch the weather. I have been across there many times in the winter and a lot of times the roads are dry and dusty...

Take a look at Amtrak. The Empire Builder route is very scenic. Reserve a private room, it's a nice relaxing way to travel. Gourmet meals are included, and they used to do a champagne reception to kick off the trip, don't know if that still happens.

You can get on an bus anywhere in Southern Michigan and it will take you to Union Station downtown Chicago, or if you're on the west coast of Michigan, you can board the train as far North as Grand Rapids.

On the road across the northern tier at the end of November? I wouldn't. The possibility of maybe needing to chain up crossing the Cascades is enough to make me get plane tickets, not to mention the same possibilities in the Rockies and Bitterroots in Montana and Idaho. And how about a blizzard in the Dakotas? Some would say, "Stop in place and wait it out." Way to many intangibles that time of year for me. I would be researching plane tickets.

I think you would be OK. Give yourself extra time if the weather would turn bad.
Without chains you might have to wait extra day for roads to clear if a storm pops up.

Not a good idea, driven Minneapolis to Seattle many times, in both the motor home and jeep - there are some huge mountains on the interstate in western Montana

And I am not a chicken to drive in the mountains ever except winter