Canada is a wonderful country....I'm biased of course, however, the weather can be SO very unpredictable, that you'd likely be "safe" at Disney in Florida, HOWEVER, IF your kids are NOT at least 8 or 9, they WON'T appreciate the park venues at Disney.
Just got off the phone with Sonia at FlowerBuyer, she just got back from San Fransisco, and would easily recommend you guys do San Fran again!!
Also, would you consider Costa Rica, that time of the year...it's absolutely kid friendly, and you will experience things that you cannot experience anywhere else on this planet!!