Even when it just had a director and two principal actors in place, Disney’s upcoming Saving Mr. Banks already seemed like it was the perfect storm of mainstream appeal. Take director John Lee Hancock, who made mountains of money and received boatloads of acclaim for his sugary sweet The Blind Side, give him two of the most universally loved actors working in Tom Hanks and Emma Thompson, and put them to work on subject matter involving one of the biggest legends in entertainment history, Walt Disney, and one of the most enduring children’s stories of all time, “Mary Poppins,” and you have to imagine this film’s potential for box office dollars and warmed hearts is unprecedented. It turns out Saving Mr. Banks isn’t just content to get our attention and then sit back and coast on a winning formula though. Variety has a new report that a trio of actors have just signed on to the film in supporting roles, and they’re three of the best supporting players studio dollars can buy. Joining Tom Hanks as Walt Disney and Emma Thompson as “Mary Poppins” author P.L. Travers will be Paul Giamatti, Jason Schwartzman, and Ruth Wilson.