HU 300 BB deep 3suited board with flopped set how to play

[FiSheYe]

I don't think there is anything else than 4bet push
QQ or Flush are your concern.
Set over set is too rare to be really taken into account on this board he could easily have
AhQx here and I can't see you getting away especially if you describe him as donkish and not a supernit.
Just get it in on the flop and hope for the best