Mix garlic, Aleppo, salt, and sugar in a small bowl; rub over pork. Place in a large roasting pan. Cover and chill 12-24 hours. Preheat oven to 300°F. Uncover pork and roast, basting with drippings every hour or so and covering with foil if browning too quickly, until an instant-read thermometer inserted into the thickest part of pork registers 145°F (meat will be very tender but not quite falling off the bone), 6-7 hours. Transfer to a cutting board and let rest at least 30 minutes before slicing. Do ahead: Pork can be roasted 1 day ahead. Let cool; cover and chill. Reheat in a 225°F oven (about 1 hour). Whisk shallots, vinegar, parsley, marjoram, Aleppo pepper, oil, sugar, and 2 tablespoons water in a medium bowl. Season with salt and black pepper; serve with pork. Do ahead: Vinaigrette can be made 6 hours ahead. Cover and chill.