I strongly believe that Su's father could actually be Sokka. Not just because she looks so much like him, though look closely at her facial expression and think about Sokka making that exact reaction.
It has been clarified that Lin and Su are half sisters. It has already been said that Kanto was Lin's father and that the relationship didn't work out. It only makes sense that if Sokka was a father to one of Toph's daughters, that he would be Su's.
Here's some more reasons as to why this is even possible:
- when it comes to making strategies Su is really good at them just like Sokka.
- When she was younger she was as sarcastic as Sokka. lastly...
- Su's second oldest son, Huan Beifong reminds me too much of constantly annoyed Sokka, or Sokka trying to think of a new sarcastic comment to make..