You hit 12 against a dealer's 2 or 3. The dealer's 2 is called the "Dealer's Ace", because it has so much potential. You will bust a 12 31% of the time, so you will not bust 69% of the time. It's a slam dunk.
I'll mainly follow with basic strategy. However, I like to stand on 12 when dealer shows a 6 or less [even if it's a 2 or 3]. My vote is to hit if Dealer shows a 7, 8, 9, 10, or Ace. If the Dealer was showing a 3, what are the chances I'll bust? What are the chances I won't bust?