Grease a 9x13 inch baking dish with butter or nonstick cooking spray.
Add the cubed bread, cream cheese and blueberries to the pan and toss to combine.
In a large bowl, mix the eggs, milk, cinnamon, vanilla extract, and syrup. Pour over the bread. Cover, and refrigerate overnight.
When you are ready to eat remove from the refrigerator while the oven is preheating.
Preheat the oven to 350 degrees.
Cover and bake for 30 minutes. Uncover and continue baking for 30 minutes, until golden brown and the center is no longer giggly.
Blueberry Sauce
Add sugar, cornstarch and water to a medium saucepan. Bring to a boil and whisk constantly for 4 minutes. Add in the blueberries, reduce heat and simmer until the blueberries burst and the sauce is thickened, 8-10 minutes.
Serve immediately with the french toast casserole.