YES you can do doggie CPR!!!
If you are so inclined
Mouth to muzzle is not that hard, Hold the dogs mouth closed and blow in to the nose.
The chest compressions are quite abit harder on a full grown large dog like a lab. but it is done much the same as on a human, pump the rib cage dog laying on the back so on...
I can't believe this knolage is being applied on a site like this...
I used to raise show dogs nad learned to do this from a vet, comes in handy when trying to save 3000$ puppies after birth.
You best bet is getting a good Doggie PFD and using it EVERY Time your friend is on the river, Would you let ME swim in white water with out one????
Dogs are really good swimmers by nature but getting held in a hole is not normal swimming for anyone!!!!