McAdams, 34, is in talks to star in an upcoming Cameron Crowe flick which also stars Cooper and Emma Stone, reported E! online.
Cooper, 38, who is dating model Suki Waterhouse, spent the time flirting and laughing with McAdams over their meal.
"Bradley would not take his eyes off her," a source said.
Later, both Cooper and McAdams took a break from their meal to pose for photos with some excited fans and staff of the local coffee spot.