Huh well it would to early for a Man of Steel sequel, and I doubt they will reboot the Batman series that soon. So maybe Green Lantern 2? or RED 2? A Justice League movie is still years away but a Flash movie could kick start it. I really don't know what DC is going to do after Man of Steel.
(I'm surprised this fight has not been done before and if has and I am mistaken that I apologize.)
Victor has been following Bullseye for a few days waiting for the perfect time to attack. Bullseye is aware that someone has been following him but has been ignoring him. Then one day Zsasz attacks early in the morning in some random abandoned house that Bullseye was sleeping in.
Mr. Zsasz knows what Bullseye is capable of. Bullseye has no idea what Zsasz is capable of, but knows that he obviously wants to kill him.
Setting: Abandoned house early in the morning
Characters: Bullseye vs Zsasz (Both characters are at full strength and no one is caught of guard. Zsasz know what Bullseye is capable of and Bullseye knows nothing about Zsasz)
Weapons: Zsasz has 6 knifes and Bullseye has two sai (the kind of sword that he has in his left hand in the picture bellow.).
It will either be at the end of the movie, after he fought in WWII. As just like a flash forward to modern times thingy, or at the beginning and the rest of the story will be a flashback.
Either way it is not really a spoiler since anyone that knows Caps story knows that this will happen at some point in the movie, or that he will have to come to modern times somehow to join the Avengers.