Heat the oven to 375°F and line a rimmed sheet pan with parchment. Pour hot water over stuffing mix and let stand for 10 minutes, then fluff and cool until no longer hot.
Cook celery and onion in butter over medium heat for 7 minutes, then cool for 5 minutes.
Mix stuffing, vegetables, eggs, sage and pepper, then fold in turkey and pork. Shape a 10-by-5-inch loaf about 2 1/2 inches high.
Bake for 40 minutes. Warm cranberry sauce, mustard and 1 tablespoon water in a small saucepan over low heat, whisking smooth.
Brush the glaze over the loaf and bake for 20 to 25 minutes more until the center reaches 165°F.
Rest for 10 minutes and cut into 8 slices.