Unroll roast; trim fat. Combine sage, thyme, 1/2 teaspoon salt, and 1/4 teaspoon pepper; rub inside surface of roast with one-third of sage mixture. Reroll roast, securing at 1-inch intervals with heavy string. Rub outside surface of roast with remaining sage mixture.
Preheat oven to 425°.
Place a large Dutch oven coated with cooking spray over medium-high heat until hot. Add roast; brown on all sides. Remove roast from pan; set aside. Melt margarine in pan. Add onion and celery, and sauté 5 minutes. Return roast to pan. Combine 1/2 teaspoon salt, 1/4 teaspoon pepper, apple juice, applejack, and broth; pour over roast.
Insert a meat thermometer into thickest portion of roast. Cover and bake at 425° for 20 minutes; reduce oven temperature to 325° (do not remove roast from oven), and bake 30 minutes. Add apple; cover and bake an additional 30 minutes or until meat thermometer registers 160° (slightly pink). Remove roast from pan, reserving cooking liquid. Place roast on a platter; cover with foil. Let stand 10 minutes.
Combine water and cornstarch, and stir into reserved cooking liquid. Bring mixture to a boil, and cook 1 minute or until sauce is slightly thick. Serve sauce with pork.
Note: Use 1 cup apple juice concentrate and omit apple brandy, if desired.