Basic MOSFET question
20V (or -20V) and 2A (or -2A) is probably OK. I'd concern myself with on-resistance too.

By the way, you won't be converting 12V at 2A to 5V at 2A  - if your 5V load is 2A then the output power will be 10 watts and, given that a buck converter is 90% efficient, the input power will be 11 watts implying an input current of only 0.92 amps.