Preheat oven to 325°. For stuffing, combine the bread crumbs, water, 2 tablespoons butter, onion, parsley, salt, poultry seasoning and pepper. Place about 1/3 cup stuffing under the skin of each chicken breast; secure with toothpicks. In a shallow bowl, combine flour and paprika; coat chicken. Place in a greased 13x9-in. baking dish. Drizzle with remaining butter.
Bake, uncovered, until a thermometer reads 170°, 1 to 1-1/4 hours. Meanwhile, for sauce, heat butter in large skillet over medium heat. Add mushrooms and onion, cook and stir until tender, 2-3 minutes. Stir in the flour, salt and pepper. Whisk in cream until blended; bring to a boil. Cook and stir until thickened, 1 minute. Reduce heat; add sour cream. Stir just until heated through; do not boil. Serve with chicken.