Position a rack in the lower third of the oven and preheat to 375 degrees . In a bowl, combine the garlic, 3 tablespoons rosemary, 1 tablespoon olive oil, 1 tablespoon salt and 1 1/2 teaspoons pepper. Coat the roast with the mixture. Place in a roasting pan and position an oven-safe meat thermometer in the thickest part of the roast, away from the bone. Cook, checking the temperature after 45 minutes, until it reaches 100 degrees , about 1 hour and 15 minutes.
Meanwhile, in a saucepan, boil the pomegranate juice until reduced to a syrup, 30 to 40 minutes.
Once the roast reaches 100 degrees , baste with the pomegranate glaze. Cook the roast, basting every 15 minutes with the glaze and the pan juices, until it reaches 135 degrees , about 45 minutes (the temperature will continue to rise). Transfer to a carving board and let rest for 30 minutes.
Meanwhile, skim and discard the fat from the pan juices and stir in any leftover glaze.
In a large skillet, heat the remaining 1 tablespoon olive oil over medium heat. Add the onion, fennel and remaining 1 tablespoon rosemary. Cook until the vegetables are softened. Add the couscous and 2 1/2 cups water and bring to a simmer. Lower the heat, cover and cook until the liquid is absorbed, about 8 minutes; let sit, covered, for 10 minutes. Stir in the pecans, pomegranate seeds and parsley; season with salt and pepper.
Carve the roast, adding any carving juices to the sauce. Serve with the stuffing.