Pre-Crisis Superman is infinitely stronger than Goku. Hopefully they only use post-Crisis Superman in this fangasm.
If Superman keeps to his morals and doesn't kill, eventually Goku will win. Goku's power levels naturally increase and expand every time he's near death. He may lose the first 99 battles, but he'll always win the last one.
Contact King Kai on how to defeat Broly. Instant transmission to said location of where Kryptonite can be found. Solar Flare Supes, and shove that Kryptonite right up his candy-ass. Goku wins.