Preheat your oven to 350°F (175°C).
Pour the maple syrup into the bottom of a 9x13 inch baking dish, spreading it evenly.
In a mixing bowl, whisk together the eggs, milk, vanilla extract, cinnamon, salt, and sugar (if using) until well combined.
Place the cubed French bread evenly over the syrup in the baking dish.
Pour the egg mixture over the bread cubes, ensuring all pieces are soaked. Gently press down on the bread to submerge it fully.
Cover the dish with aluminum foil and refrigerate for at least 1 hour or overnight for the best results.
Bake the casserole covered for 30 minutes. Then, remove the foil and bake for an additional 15 minutes or until the top is golden brown and slightly crispy.
Allow the casserole to cool for a few minutes before serving. Serve warm, optionally with additional syrup or powdered sugar.