Brine the roast: In a saucepan, heat the pickling spices over low heat for 30 to 60 seconds until fragrant. Add the water and salt, stirring until the salt dissolves. Remove from heat, stir in the apple juice, and garlic. Let cool completely. In an airtight container or plastic zip bag, cover the roast with the cooled brining liquid. The meat should be completely submerged. Store overnight or 8 to 10 hours in the refrigerator.
Prepare the roast: Remove the roast from the brining solution. Rinse it well with water and pat dry with paper towels. Slice the roast along the center to butterfly it while the meat is still cold. Let it come to room temperature while you prepare the stuffing, before pounding thinner with a meat mallet.
Make the stuffing: In a large sauté pan, cook the bacon over medium-high heat until it starts to brown, about 2 to 3 minutes. Melt the butter in the pan with the bacon and add the onion, celery, and garlic. Sauté until the vegetables are soft, about 2 minutes. Stir in the brown sugar, sherry, and cranberries, reduce the heat to low, cook for 4 to 5 minutes until the cranberries are soft. Remove the pan from heat and stir in 1 minced spring of rosemary, bread, and cheese. Let cool slightly while you pound the pork roast. Preheat the oven to 375°F.
Stuff the pork roast: Layer a piece of plastic wrap over the pork roast and pound the cut thinner with a meat mallet. Place the roast with the fat cap on the cutting board side and the inside of the roast facing up. Layer the stuffing onto the roast, slightly pressing into the roast. Tightly roll the pork roast so that the fat cap ends up on the top of the roast. Tie with a butchers knot or with 6 separate pieces of butchers twine. Once the roast is tied, season generously with salt and pepper and tuck 3 springs of rosemary on top.
Sear and roast: Heat the oil in a stovetop and oven-safe roasting pan. Sear the roast for 3 minutes on the top and bottom and 1 minute on each side. Remove the pan from the heat, carefully transfer the roast fat side up to a roasting rack and place inside the roasting pan. Add the wine and chicken stock to the bottom of the roasting pan. Roast in a 375°F oven for 45 to 60 minutes, until the center of the pork reaches 145°F.
Rest and serve: Transfer the roast to a cutting board and let rest 10 to 15 minutes. Remove the butcher's twine and slice into 1 to ½ inch pieces. Serve with your favorite sides.