Prepare a casserole dish with nonstick cooking spray.
Place the bread in the prepared casserole dish in a staggered layer.
Beat the eggs until frothy. Stir in the vanilla, cinnamon, pumpkin spice, sugar, and pumpkin puree until well blended. Add the milk, stirring until completely incorporated.
Pour the pumpkin mixture over the bread.
Cover the casseroles and allow to soak in the refrigerator for at least two hours or overnight.
When ready to bake, preheat the oven to 350 degrees and place the casserole on the counter as the oven heats.
In a medium bowl, stir together the brown sugar, cinnamon, and all-purpose flour. Cut in the butter until the mixture is the consistency of coarse sand. Sprinkle over the casserole.
Bake the French toast casserole for 30 to 40 minutes or until golden brown.
Swerve with maple syrup or powdered sugar.