In a shallow bowl, whisk to blend eggs, egg whites, milk, vanilla, sugar, cinnamon, and nutmeg.
Lightly mist a 10- by 15-inch nonstick pan with cooking oil spray.
Soak bread thoroughly on each side, a few pieces at a time, in egg mixture.
Place slices slightly apart in a single layer in baking pan.
Bake in a 500° oven until toast is golden on bottom, about 5 minutes. With a wide spatula, turn slices over and bake until other side is browned, about 3 to 4 minutes longer. Transfer hot French toast to plates.
Sprinkle with powdered sugar, drizzle with maple syrup, and serve with orange wedges, squeezing juice onto toast.