Spread half of the bread cubes evenly in the prepared dish, sprinkle with 1 cup of the blueberries, then top with the remaining bread cubes and the rest of the blueberries.
In a large bowl, whisk together eggs, milk, heavy cream, sugar, vanilla extract, and cinnamon until well combined.
Pour the egg mixture over the bread and blueberries, pressing down gently to ensure the bread is fully soaked. Allow to sit for at least 30 minutes, or cover and refrigerate overnight.
Preheat the oven to 350°F. Bake the casserole for 45 minutes, or until the top is golden and the center is set.
Serve with maple syrup and a dusting of powdered sugar.