HEAT oven to 325ºF.
MELT 2 Tbsp. butter in large skillet on medium heat. Add vegetables; cook and stir 10 min. or until onions and celery are crisp-tender.
ADD hot water and remaining butter to stuffing mixes in large bowl; stir just until moistened. Chop 1/4 cup sage. Add to stuffing with vegetables; mix lightly.
FREE turkey legs from tucked position. (Do not cut band of skin.) Using rubber spatula or hand, loosen skin over breast, starting at body cavity opening by legs. Place remaining sage leaves on meat under skin. Spoon stuffing into neck and body cavities, being careful to not pack stuffing into turkey too tightly. Return legs to tucked position; turn wings back to hold neck skin in place. Place turkey, breast-side up, on rack in roasting pan. Brush with dressing. Cover loosely with foil to prevent over-browning.
BAKE turkey 3 hours 45 min. to 4 hours or until done (165ºF), uncovering after 3 hours. Let stand 15 to 20 min. before carving.