I've done the Canyon in a 14' twice. First time I was in a Hyside, second time a RMR. Both trips were all outfitted entirely with 14' or smaller boats.
Flipped three times total. Once in Crystal, twice in Upset. No major damage, but I'd rather not flip in Upset in the winter ever again. None of the flips were due to the boat; all of them were caused by me F-ing up my line.
I think the main issue is that rigging a smaller boat for a big trip takes a little more thought, but once you get it dialed, it's fine.