1 damage or 3, it's up to you
If you put Ambuscade Shaman's trigger on the stack first, then Warstorm Surge's trigger on top, then the damage trigger will resolve first and deal 1 damage to target creature or player. Then, Shaman's trigger will resolve giving the creature +2/+2 until end of turn.
If you put Warstorm Surge's trigger down first, then Shaman's trigger will resolve first, giving the creature +2/+2 until end of turn, and then Surge's trigger will resolve, dealing 3 damage to target creature in player.
Suffice to say, it's likely that you want the second scenario to occur most of the time.