For brining pork:
For roasting pork
Brine pork: Combine all brining ingredients except pork loin in a 3- to 4-quart saucepan and heat over high heat, stirring, until salt is dissolved. Pour brine into a deep 4- to 5-quart pot; cool to room temperature.
Add pork to brine, making sure it is completely covered by brine, and marinate covered and chilled for 8 to 24 hours.
Preheat oven to 350°F.
Rinse and pat pork dry (discard brine) and remove any strings, then transfer to a roasting pan. Stir together garlic, sage, shallots and 1 tablespoon syrup in a small bowl and rub all over pork. Lay bacon slices crosswise over loin, overlapping slightly, and tuck ends of bacon underneath loin.
Roast pork until thermometer registers 140°F, about 1-1/4 hours. Stir together 1 tablespoon syrup and vinegar until combined. Brush vinegar mixture over bacon slices and continue to roast pork until thermometer registers 150°F, about 10 minutes more. Broil on high for 3-6 minutes if bacon isn’t crispy enough. Remove from oven and let rest in pan 15 minutes.
Transfer roast to a cutting board, reserving juices in pan.
Skim fat from pan juices and discard, then transfer jus to a small saucepan and bring to a simmer,add wine if desired. Stir together cornstarch and water and whisk into jus. Simmer, stirring, until slightly thickened, about 1 minute. Remove from heat and stir in remaining tablespoon syrup. Serve pork with sauce.