Nah, you wouldn't break your wrist, because you wouldn't be blocking it, you would be deflecting it. Very little of the hammer's force would be transferred to you wrist, all you need to do is change its course a tiny bit to successfully deflect. Of course it wouldn't be easy or something you'd realistically do all the time, but it's possible.
Not to mention that this goes both ways: good luck blocking a flurry of attacks from a fast one-hander with a heavy great maul in real life.