Preheat oven to 350 degrees F.
Place pumpernickel bread on a large baking pan and crumble into coarse crumbs. Bake, stirring once, 12 to 15 minutes or until lightly toasted. Set aside. Increase oven temperature to 450 degrees F.
Melt butter in a large skillet over medium heat. Add onion and cook, stirring often, 5 minutes or until softened. Stir in garlic and cook 1 minute. Remove skillet from heat and stir in toasted pumpernickel crumbs, red cabbage, raisins, 1/4 teaspoon salt and 1/4 teaspoon pepper.
Make a cut lengthwise down the center of the pork, cutting to, but not through the bottom. Open the butterflied portions, laying pork flat. Starting from the center of each half, slice lengthwise down the center of the pork, cutting to, but not through the bottom. Unfold pork so it lies flat. Place plastic wrap over meat and flatten to 3/4-inch thickness using a meat mallet or rolling pin.
Sprinkle top of pork with 1/4 teaspoon salt and 1/4 teaspoon pepper and spread with 3 tablespoons Bavarian mustard. Spread the stuffing mixture evenly over pork and roll up, jellyroll fashion, starting with the long side. Secure with string and place seam side down in a shallow flameproof roasting pan.
Sprinkle outside of pork with the remaining 1/4 teaspoon salt and 1/4 teaspoon pepper and brush with 2 tablespoons remaining Bavarian mustard. Bake for 20 minutes. Reduce oven temperature to 350 degrees F. Bake 25 to 30 minutes, or until a thermometer inserted diagonally 2 inches into pork (do not touch stuffing) registers 150 degrees F. Transfer pork to a serving platter, cover loosely with foil, and let stand 15 minutes or until thermometer registers 160 degrees F.
Place roasting pan across two stovetop burners over medium heat. Whisk together the chicken broth, wine and flour in a medium bowl and whisk into the pan drippings. Cook, whisking constantly, for 5 minutes, until mixture comes to a boil and thickens. Stir in remaining 1 tablespoon Bavarian mustard and remaining 1/4 teaspoon pepper. Serve sauce with sliced pork loin.