This is the cartoon versions of each team.
Avengers: Iron man
Justice League: Superman
1st Round: Random encounter, in New York, civilians are present.
2nd Round: Each Team gets 10 hours of prep, can use all resources available (but not any extra help, for example. Black Panther may be able to use Wakkanda Tech, but is not alowed to bring his warriors). fight is in New York with civilians.
3rd Round: The Avengers have to take out the Legion of Doom (From the cartoon movie), and The Justice League has to take out the Masters of Evil. First team to complete the task wins. And also, how would each team take them down?
Legion of Doom: Cheetah
Masters of Evil: Zemo
Morals are on, so both teams will be careful not to hurt civilians