Unless another team enters into the equation with a late bid, the deal could be finalized by early next week.
Matt Wieters is the Orioles' top prospect, but they need some protection for the position until Wieters is ready to take the job.
Earlier this offseason, the Orioles signed free agent Chad Moeller. Should they ink Zaun, he would be the starter in the absence of Wieters.
Zaun, who began his Major League career with the Orioles in 1995, hit .237 with six home runs and 30 RBIs for the Blue Jays in 2008.
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.