In a small bowl, combine soy sauce and mustard; rub over roast.
In a shallow bowl, combine fennel and caraway seeds; coat roast with roast. Cover; refrigerate for at least 2 hours.
Place roast fat side up on a rack in a shallow roasting pan. Bake, uncovered, at 325° for 1 hour and 20 minutes or until a thermometer reads 160°. Cover and let stand for 10 minutes.
For sauce, in a small saucepan, combine the mustard, cornstarch and water until smooth. Stir in corn syrup and vinegar. Bring to a boil; cook and stir for 1-2 minutes or until thickened. Serve with roast.