Cut or tear cake into 1/2-in. pieces to measure 8 cups. Place half the cake cubes in a 9-in. square dish. Set aside 1/3 cup of pie filling; spread remaining filling over cake. Top with remaining cake cubes.
Combine the pudding mix, milk and sour cream. Spoon over cake. Cover and chill. To serve, cut into squares and top with reserved cherries.