Brown the maple sausage on medium high for 5 minutes, until browned. You want to get some good color on it for flavor. Add the butter, celery, red onion, apple, cranberries and ground sage to the pan you cooked the sausage in. Sauté over medium heat for 8 minutes.
Set the slow cooker to low. Lightly coat with cooking spray. Add water to the slow cooker, then add the boxed stuffing mixes. Lightly stir. Add remaining ingredients and stir well. Cover and cook on low for 3 hours, giving it a stir every hour. When ready to serve, garnish with fresh Italian parsley.