Melt butter in a large skillet over medium heat; add onion and garlic, and sauté 5 minutes or until tender. Add sausage, and cook, stirring until it crumbles and is no longer pink; drain. Stir in apple and celery, and cook, stirring occasionally, about 10 minutes. Transfer mixture to a large bowl.
Stir in raisin mixture, croutons, and remaining ingredients until moistened. Spoon into a lightly greased 13- x 9-inch baking dish.