Preheat oven to 350°.
Remove and discard giblets and neck from turkey. Rinse turkey with cold water; pat dry. Trim excess fat. Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers, gently pushing between skin and meat. Rub Cajun seasoning and salt under loosened skin, and sprinkle in body cavity. Tie ends of legs with cord. Lift wing tips up and over back; tuck under turkey.
Place turkey on a broiler pan coated with cooking spray or on a rack set in a shallow roasting pan. Insert meat thermometer into meaty part of thigh, making sure not to touch bone. Bake at 350° for 2 1/2 hours or until thermometer registers 180°. (Cover turkey loosely with foil if it gets too brown.) Remove turkey from oven. Cover loosely with foil; let stand 10 minutes before carving. Discard skin. Serve with Dirty-Rice Stuffing. Garnish with parsley and rosemary sprigs, if desired.