It's a violation of both, but my inclination would be to fix "hold" first. To your second question, I would hit the sit whistle the instant he spit the bird/bumper, then walk up to him and put it in his mouth, reinforce "hold", then walk back several yards and whistle him to me. (Note that, like Gooser said, his whistle sit has to be 100% or none of this is works.) Next time I would meet him at water's edge, and say "hold" as I walk backwards from the water a few yards. Repeat often, gradually extending the distance from handler to water. Once this is rock solid, introduce a diversion on water.
And I would nick to "here" and then ear pinch back to the bird...if the dog is thinking about coming here he ain't thinking about hold.