Katara wins if Captain America has no gun.
Btw for the people saying the current Captain America is good with cold since he used to be the Winter Soldier, IT DOESN'T MATTER!
It just means he won't die when he gets frozen, but he is still immobilized.
The only reason anyone would say Captain America with no gun wins is cause of PIS and the fact this is posted in a freaking Comic Book forum and not a more reasonable one where people aren't biased.
If you put Iceman, remove his ability to live after turning into vapor or liquid form, people would be screaming SPITE and saying Bobby is too overpowered to face Captain America even without the fact Bobby can survive in the other two forms.