1Discard loose fat from goose. Remove neck, cut into large pieces, and reserve. Rinse goose inside and out, and pat dry. Pierce skin of goose all over, and season with salt and pepper.
2Loosely pack neck cavity with enough bread to fill out cavity. Fold neck skin under body, and fasten with a small skewer. Quarter 1 onion and all the celery, and place inside the body cavity of the goose. Tie legs together loosely with kitchen string, or insert legs through slit in lower skin flap. Transfer goose, breast side up, to a rack set in a deep roasting pan.
3Cut remaining 2 onions and carrots into 2 inch pieces. Scatter onion and carrot pieces, neck pieces, and giblets in roasting pan. Roast goose at 425 degrees C (220 degrees) in the middle of the oven for 30 minutes.
4Reduce temperature to 325 degrees F (165 degrees C). Carefully pour boiling water over goose; juices may splatter. Continue roasting goose, skimming off fat and basting with pan juices using a metal bulb baster every 20 minutes. Cook for 2 to 2 1/2 hours more, or until a meat thermometer inserted in fleshy part of thigh registers 175 degrees F (80 degrees C). When done, the juices should run clear when thigh is pierced with a skewer.
5Transfer goose to a heated platter. Remove skewer and discard string. Keep goose warm, loosely covered with foil, until ready to serve.
6With a slotted spoon discard vegetables, neck pieces, and giblets from pan. Spoon off fat from pan juices, and reserve. On top of stove, deglaze pan with white wine and port over moderately high heat; scrape up brown bits. Add chicken broth, and boil mixture until reduced by about half. In a 3-quart heavy saucepan, whisk together 1/4 cup reserved fat and flour; cook roux over moderately low heat, whisking to prevent lumps. Whisk chicken broth mixture into the roux. Bring gravy to a boil, whisking constantly. Turn down heat. Simmer gravy, whisking frequently, for 5 minutes or until thickened. Season gravy with salt and pepper. Transfer gravy to a heated sauceboat.