ChristiaanJ - it's on record that the birds were seen before impact and identified as such... I'm not sure Sully got as far as twenty-and-three before they hit though...
And even if he did get to twenty and three, does snapping the side stick of an A320 into a dive or a roll get you that immediate and dramatic response? What is the computer going to think you are doing, and is it going to allow such a drastic manuever?