Lots of Canon photographers are leaving for Sony cameras and I am not surprised. The Sony a9 is an impressive camera and offers a unique shooting experience that you simply can’t get with a Canon or Nikon camera today. Canon/Nikon’s first generation professional mirrorless cameras will be competitive, but I highly doubt it and their native mirrorless glass selection will be very limited, while Sony continues rounding theirs out with lenses like the Sony FE 400mm f/2.8 GM OSS.
Sony a9: B&H Photo / Amazon / Adorama
Comparison from Camerasize.com