Rinse turkey well and pat dry. Season cavity generously with salt and pepper. Place onion and orange wedges in cavity along with the rosemary sprigs and thyme sprigs.
Pull turkey neck skin to back; fasten with skewer. If a band of skin crosses the tail, tuck the drumsticks under the band. If there is no band, tie drumsticks securely to tail. Twist wing tips under the back.
Place bird, breast side up, on rack in a shallow roasting pan. Brush skin lightly with oil. Insert a meat thermometer into center of one of the inside thigh muscles, but not touching bone. Cover bird loosely with foil, leaving air space between bird and foil. Roast in a 325 degree F oven about 3-3/4 hours total. After 2-1/2 hours, cut band of skin or string between drumsticks so thighs will cook evenly. Continue to roast, covered with foil, about 20 minutes more or until thermometer registers 160 degree F.
Stir together orange juice concentrate, the 3/4 cup chicken broth, and the melted margarine or butter. Remove foil; brush some of the orange mixture over bird. Continue roasting, uncovered, until meat thermometer registers 180 degree F, brushing some of the remaining orange mixture over bird every 15 minutes. Reserve any remaining orange mixture for gravy. (When bird is done, the drumsticks should move easily in their sockets and the thickest parts of the drumsticks should be very soft when pressed.)
Remove turkey from oven and discard ingredients from cavity. Transfer turkey to a platter and let stand, covered with foil to keep warm, for 15 to 20 minutes before carving.
Meanwhile, to make the gravy, strain juices from roasting pan into a large glass measure. (Also scrape the browned bits into the cup.) Skim off and discard fat. Add the remaining orange mixture to juices in measuring cup. Measure liquid and add additional chicken broth, if necessary, to equal 3 cups. Pour juices into a medium saucepan. Add snipped or crushed rosemary. Combine cornstarch and the remaining 1/4 cup chicken broth. Add to saucepan. Cook and stir over medium heat until thickened and bubbly; cook and stir for 2 minutes more. Season to taste with additional salt and pepper. Remove from heat.
Just before serving, garnish platter with candied fruit slices and/or fresh fruit, if desired. Pass gravy with turkey. Makes 10 to 12 servings.