08/18/2011 AT 6:50 PM ET
The Proposal costars – who a source has told PEOPLE are “like brother and sister” – made their way to Rendezvous Bistro in Jackson Hole on Sunday.
Sans Bullock’s baby son Louis, who accompanied the actress, 47, and Reynolds, 34, on the trip, the duo joined two other guests for what a source says appeared to be a “really informal” meal.
“They didn’t seem like they were a couple,” the source says. “It was very relaxed, totally friendly. She wasn’t romantic with anyone at the table.”