reheat oven to 350. Prepare a 9 x 13" pan with cooking spray; set aside. In a mixing bowl, combine cake mix, whipped topping mix, and baking powder. In another mixing bowl, combine water, egg whites, oil, and vanilla extract. Mix dry ingredients with wet ingredients just until moistened. Spread mixture into prepared pan. Bake for 25 minutes or until golden brown. To prepare topping, combine cream cheese and half cup milk. Mix until smooth. Add remaining milk and pudding mix. Mix well and let stand until thickened. Spread over cooled cake. Spread cherry pie filling evenly over top.