In a bowl, whisk together 1 cup (250 mL) cider, melted butter and thyme. Place bowl in freezer until mixture thickens, about 30 min. Preheat oven to 350°F (160°C). Place turkey, breast side up, on a wire rack set in a roasting pan.
In a large bowl, toss together apples, onion, celery, garlic, sage and maple syrup. Set aside. Gently loosen skin of turkey from breast meat using fingers. Rub half of the cooled cider mixture under skin. Rub remaining mixture all over outside and in cavity of turkey. Season turkey with salt and pepper then fill cavity with apple mixture. Scatter remaining apple mixture around pan, along with neck and giblets. Tie drumsticks together with twine and tuck wings back under bird.
Pour remaining apple cider into pan. Set roasting pan on middle rack of oven and roast, 1 hour. Cover with foil and roast, occasionally basting with pan juices, for another 2 to 2 1/2 hours, or until a meat thermometer reads 185°F (85°C) when inserted into the thickest part of the thigh, away from the bone. Remove turkey from oven, discard apple mixture, loosely over with foil and let rest 15 min. before carving and serving.