Kettlebells work better than dumbbells for flyes. Because of the position of the resistance, the pecs are under load for a greater proportion of the range of motion.
With dumbbells, the muscle tension on the pecs is greatly reduced at about 60% of the range of motion. This can make the reps less effective, especially when you're using a method where you must maintain constant tension to create an occlusion effect.
What is it about Canada and great strength coaches? For some unknown reason, the Great White North produces some of the world's best coaches and trainers, with Charles Poliquin, Christian Thibaudeau, and Charlie Francis being just a few examples. Now, another young Canadian is beginning to climb into the ranks of the elite: John Paul Catanzaro.