Spray a 9x13-inch baking pan with cooking spray. Place the bread slices in the pan in layers and set aside.
In a medium bowl, whisk together the milk, heavy cream, sugar, eggs, pumpkin, vanilla, and pumpkin pie spice. Pour the milk mixture over the bread slices, pushing the bread down so that they absorb the liquid. Cover with plastic wrap and refrigerate overnight.
The next morning, heat oven to 350ºF. Remove the plastic wrap and scatter the cranberries over the top of the French toast bake, trying to tuck them into as many crevices as possible. Bake for 45-55 minutes, or until cooked through and set. Serve warm with maple syrup, butter, and powdered sugar.