Cut a pocket in veal breast, or ask your butcher to do it for you. Season pocket with salt and pepper. Preheat oven to 325 degrees. Set aside veal to reach room temperature.
In a skillet melt butter over medium-high heat. Add onion and celery and saute until onion is tender and golden. In a bowl combine bread and eggs; add onion mixture, parsley and 1 cup of the chicken stock. Season with salt and pepper; mix well. Stuffing should be fairly wet; add a little more chicken stock if needed.
Using a long spoon, reach deep inside veal pocket to distribute stuffing evenly. Use a trussing needle and string to sew up pocket. Season roast on all sides with salt and pepper and liberally sprinkle top with paprika. Place in roasting pan, top side up, and roast 3 1/2 hours in all. Baste top with 1/2 cup chicken stock every 45 minutes.
Remove roast to a carving board and let sit, loosely covered, 15 minutes while you prepare sauce. Set roasting pan over medium-high heat and add remaining 3 cups chicken stock. Deglaze pan, scraping up browned bits and incorporating them into stock. Boil until stock reduces to 1 1/2 cups. If desired, thicken sauce with arrowroot or butter, or leave as is. Cut center portion of veal breast along chine bone separations into 6 servings. Spoon gravy over each portion.