Preheat oven to 350. Prepare a 13"x9" pan with cooking spray; set aside. To prepare topping, combine pecans, brown sugar, flour, cinnamon. and margarine in a small bowl. Mix well and set aside. Meanwhile to prepare cake, combine cake mix, granulated sugar, cream cheese, egg whites, oil, and water in a mixing bowl. Mix until all is moistened. Spread batter into prepared pan. Scatter blueberries evenly overtop. Sprinkle topping mixture evenly over all. Bake for 50 minutes, or until toothpick inserted in center comes out clean.