Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter or cooking spray.
In a large mixing bowl, whisk together the eggs, milk, vanilla extract, cinnamon, salt, and maple syrup until well combined.
Layer half of the cubed bread in the bottom of the prepared baking dish. Sprinkle half of the blueberries over the bread.
Pour half of the egg mixture over the bread and blueberries. Repeat the layers with the remaining bread, blueberries, and egg mixture.
Press down gently on the casserole to ensure the bread absorbs the egg mixture. Cover the dish with aluminum foil and let it sit for 15 minutes.
Bake covered for 30 minutes, then remove the foil and bake for an additional 15-20 minutes, or until the top is golden brown and the casserole is set.
Allow the casserole to cool for a few minutes before dusting with powdered sugar and serving with extra maple syrup.