Pawnstoppers

I lost a Classical French yesterday (Black side), so I'm reviewing some Grandmaster games from old Chess Informants. This ending caught my eye.

Black to move

This position is from Hjartarson,J -- Seirawan,Y, Reykjavik 1991, Informant 52/282.

Seirawan played 62...d3 and a draw was agreed. How would play proceed if he had played 62...a2 instead?