Mash cranberry sauce with a fork or a potato masher. Stir in sugar, cranberry juice, mustard, and cloves.
Place pork roast in a large, roasting pan. Pour cranberry sauce mixture over the roast.
Cook at 275 degree F (135 degrees C) for 6 to 8 hours, or until meat is tender. Remove roast, and keep warm.
With a metal spoon, skim the fat from the liquid in the roasting pan. Pour 2 cups of the remaining roasting liquid (add water to fill out the measure if necessary) into a small saucepan. Bring to a boil over medium-high heat. Blend cornstarch and cold water to make a paste; stir gradually into boiling liquid. Continue cooking, stirring constantly, until mixture thickens. Add salt to taste. Serve with the roast.