The average high for Orlando in November (according to Yahoo! weather) is 79 degrees. I think you would be safe for the first half of the month. We were in WDW just after Thanksgiving last year and the temp was in the upper 70s/lower 80s. The following week, it was cooler (mid-60s).
Many of the resort pools are heated but I don't think the water parks are. Also, usually one of the water parks is closed for refurbishment by the time Thanksgiving rolls around.