Arrange bread slices on a cooling rack and allow to dry at room temperature for 30 to 60 minutes.
Meanwhile, coat a 3-quart rectangular baking dish with nonstick cooking spray. In a small bowl, beat cream cheese, maple syrup, and cinnamon with a mixer until smooth. Fold in 2 cups blueberries.
Arrange 4 slices of bread in prepared dish; spread cream cheese mixture over bread. Top with remaining bread.
In a medium bowl, whisk together half-and-half, eggs, and vanilla. Pour over bread. Cover and refrigerate, 8 hours to overnight.
Remove dish from refrigerator. Preheat oven to 350 degrees F.
Bake French toast, covered, for 20 minutes. Uncover and bake 20 minutes more, or until top is golden brown.
Let stand at room temperature for 15 minutes. If desired, top with additional berries and confectioners' sugar.
