Am I correct in assuming you are interested in Williamsburg for the history, and not the theme park? I can tell you that Busch Gardens - one of the world's great amusement parks - will be open that time of year Fridays through Sundays from 10AM-10PM, with special Halloween activities. My wife and I visit every year (just got back, in fact) and love it. It is very family-oriented, although it does have its share of top-notch thrill rides, and a couple of the best roller coasters anywhere.
I don't know much about the Colonial part, although you can find out a bunch on the internet. Either way the area is chock full of hotel options. In the past we swore by the Radisson Fort Magruder on Pocohontas Trail
http://www.ichotelsgroup.com (down the road from Busch Gardens, a few minutes from Colonial Williamsburg) - it switched affiliations this year and is now a Crowne Plaza - but still has indoor and outdoor pool, restaurant and lounge, and even tennis courts. We usually paid about $100 U.S. a night with CAA discount. This past trip, however, we splurged and stayed at the Kingsmill Resort
http://www.kingsmill.com/ a huge, gorgeous full-service resort, with several golf courses, tennis, spa, recreation facility including pools, saunas, games room, racquetball, etc, etc. Service was extraordinary - not stuffy at all - and they even offer regular, free shuttle service to all area attractions. It is not cheap, but they do offer packages for families that include tickets to the park (plus a meal for everyone), complimentary use of their championship golf courses, and several other perks.
There's also a brand-new Great Wolf Lodge in the area (
http://themeparks.about.com/od/usindoorwaterparks/p/GreatWolfVA.htm); I've never stayed at one - they're well-regarded (and expensive) hotels built around a rustic theme and indoor water-park.
Hope some of this helps. In any event, Virginia offers discount coupons to Canadian visitors at
http://www.looniesavers.com/. Whatever you decide, I have one piece of advice - at all costs, avoid the I-95/495 "beltway" around Washington any time between 6AM and 8PM during the week. It makes the 400 northbound on a Friday afternoon of a long weekend look like a superspeedway ...