Preheat oven to 425. Prepare a 8" x 8" dish with cooking spray; set aside. In a skillet, cook celery and onions until tender. Remove from heat. Stir in stuffing cubes, salt, poultry seasoning, and black pepper. Drizzle broth half cup at a time to moisten, tossing lightly. Spread mixture into prepared dish. Bake for 30 minutes, or until browned on top.