Coat a large nonstick skillet with cooking spray. Add sausage, and cook 5 minutes or until browned on all sides. Remove sausage from skillet, and set aside. Add chicken to skillet, and cook 7 minutes on each side or until chicken is done. Remove chicken from skillet, and let cool slightly. Shred chicken; set aside.
Place flour on a baking sheet; bake at 350° for 20 minutes or until dark brown, stirring occasionally.
Coat a large Dutch oven with cooking spray; add oil. Place over medium-high heat until hot. Add celery and next 4 ingredients; saute 8 minutes or until tender. Add browned flour, Creole seasoning, and next 4 ingredients, stirring well. Add broth and sausage. Bring to a boil; reduce heat, and simmer, uncovered, 1 hour. Add chicken, and simmer, uncovered, 30 minutes. Remove and discard bay leaves. Stir in file, if desired. To serve, place 3/4 cup rice in each of 8 bowls; ladle 1 1/2 cups gumbo over each serving.