Philly.com is reporting that Katharine Houghton has been cast as Kanna, affectionately known as Gran Gran to her grandchildren Sokka and Katara, in The Last Airbender. Houghton is best known for her role as Joanna “Joey” Drayton in the socially groundbreaking film, “Guess Who’s Coming to Dinner,” which dealt with the controversial subject of interracial marriage.