If I fell out of my canoe, I wouldn't worry about my revolver until I had time to clean it. They've been proven to be good for swimming with. But when I went to clean it, I would remove the stocks, relieve the mainspring and pop the side plate. Then I'd clean it out with a gun cleaner (Ballistol or Breakfree). I like to use compressed air to blast cleaner/oil out of the lockwork since it's not easy to get a patch or brush in all those places. I would not fully strip it just for water, but I would pop the side plate. If it was salt water or silty, I'd be more inclined to fully strip it.
As for the ammo, I expect it would be fine in the short term after a short dunk. The longer it soaked the less I'd want to depend on it. And any carry ammo that gets wet should be replaced when possible. Some people lacquer the primers and crimp, but I have not seen evidence this improves results. Again, I would expect dunked ammo to work in the short term. If its soaked for a long time, why depend on it when you can change it out?
I have had primers and powder each fail as a result of water, but the water was in the case when I loaded them (insufficiently dried brass). Wet powder produced a squib and barrel obstruction, so I know the consequences can be serious. Shoot any wetted ammo very carefully and if you can change it out, all the better.