Combine first 10 ingredients in a large shallow dish or zip-top plastic freezer bag; add pork. Cover or seal, and chill 8 hours, turning occasionally.
Remove pork from marinade, reserving marinade to equal 2 1/2 cups, adding water if necessary. Place pork on a rack in a shallow roasting pan lined with aluminum foil.
Whisk reserved marinade into cornstarch in a small saucepan. Place pan over medium-high heat, and bring sauce to a boil, whisking constantly. Cook, whisking constantly, 2 to 3 minutes or until thickened. Remove and reserve 1/4 cup sauce. Set remaining sauce in saucepan aside.
Broil pork 6 inches from heat 5 minutes. Pour 1 1/2 cups water into bottom of pan. Reduce oven temperature to 325°, and bak 1 hour and 15 minutes to 1 hour and 30 minutes or until a meat thermometer inserted into thickest portion registers 155°, basting with reserved 1/4 cup sauce during the last 15 minutes. Remove roast, and let stand at least 10 minutes or until meat thermometer inserted into thickest portion registers 160° before slicing. Serve with remaining warm sauce.