Roast uncovered 3 hours to 3 hours 30 minutes (if necessary, place tent of foil loosely over goose during last hour to prevent excessive browning), removing excess fat from pan occasionally. Meanwhile, spray 2-quart casserole with cooking spray. In 3-quart saucepan, melt butter over medium-high heat. Cook celery and onion in butter, stirring occasionally, until tender; remove from heat. Stir ¡n remaining ingredients except gravy. Spoon into casserole. Cover and refrigerate until baking time.