You can't really replace the effect of a polarizer in post. On the other hand, depending on what you want to show in the image you may not want to use one. Polarizers also reduce reflections on the surface of water so you have to make some choices and compromises. More often than not on a shot like the one posted I wouldn't use one at all. If there is underwater structure I want to be able to see in the image then you might need one with the full or partial effect.
You could do a shot with and a shot without and then blend them. At least with something like that shot.
But yeah, Polarizer and ND's aren't really capable of being added in post - with ND the subject movement, not exposure difference.