My son did and loved the Grand Floridian adventure, however he got something a little different than they normally do.
It was RAINING the day of his adventure, but we went ahead and showed up because we were unsure of whether they cancelled for rain and stuff.
They don't.
Instead of going out on the water they went around the Grand Floridian with their maps and looked for clues to the treasure.
I was a bit dissapointed that he wouldn't get to go sailing. . . BUT he still LOVED it and it totally put him in a good mood for the rest of the day.
So, as a note, they don't cancel for rain.