The industry trade papers report that both actors are still in negotiations to topline the project, which would be set up at 20th Century Fox.
In addition, veteran "Entourage" director Julian Farino would direct from the script by Dana Fox.
Who really needs a plot when you've got the Vegas tourism motto as your title? "What Happens in Vegas" would feature Kutcher and Diaz two people who discover they've gotten married after one wild night in Sin City. They also discover that they each won a jackpot playing a quarter for the other. Can they get each other's loot or will they just fall in love?
You can hear Diaz in "Shrek the Third," opening this weekend. The actress was most recently seen in "The Holiday" and "In Her Shoes."
For his part, Kutcher is too busy being a television impresario to both acting. The man behind "Beauty and the Geek," "The Real Wedding Crashers" and ABC's upcoming "Miss/Guided" last starred in "The Guardian" and in a vocal capacity in the animated "Open Season."