Preheat the oven to 400°F. Cut the French bread into ½-inch cubes. Arrange the cubes in a single layer on 2 sheet pans.
Bake the bread cubes for 10 minutes, or until lightly browned. Let cool.
Reduce the oven temperature to 375°F. Spray a 13 x 9-inch baking dish with nonstick cooking spray.
Spray a skillet with nonstick cooking spray, and place over medium-high heat.
Add the onion and celery to the skillet, and sauté for 5 minutes, or until onions are translucent and celery is almost tender.
In a large mixing bowl, combine the chicken broth, sage, thyme, onion powder, salt, pepper, and poultry seasoning. Add the toasted bread cubes to the bowl, and quickly toss until nearly all the liquid has been soaked up by the bread.
Add the sautéed vegetables to the cubed bread in the mixing bowl, and toss to combine. Transfer to the prepared baking dish.
In a small bowl, whisk together the egg whites and melted butter. Drizzle over the stuffing in the baking dish.
Cover with aluminum foil and bake for 25 minutes. Remove aluminum foil and bake for an additional 20 minutes, or until the top of the stuffing begins to brown. Let cool for 5 minutes before slicing. For 100 calorie portions, slice into 12 sections by cutting 3 rows by 4 rows.