Ryan Reynolds and Sandra Bullock at The Change-Up premiere in L.A.
08/18/2011 at 06:50 PM EDT
and Ryan Reynolds
's visit to Wyoming
last weekend also included a low-key dinner with friends.
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."