I just did that trip. Whistler is 6 hours away (I was told). Your realistic choices are AlpentaI, Stevens Pass, Snoqualmie or Chrystal Mountain. I did Chrystal Mountain, which is less than 2 hours from Seattle, but it's huge and steep by Eastern standards, and it has great views of Ranier. I stayed at the Alpine Inn, which was cheap, but the bar was friendly,the restaurant was pretty good, and the location was perfect.
Conditions have been pretty sketchy throughout the Northwest this year, but Chrystal was way better yesterday than it was on Monday. Chrystal is really generous to PSIA/NSP members as well, so bring your card if you have one.
Plan on renting skis. You may want anything from a slalom ski to a full rocker, depending on what day you are there. You'll want yellow goggles as well.
It's all about the conditions, and you don't really need to make a decision until you get there.