Grease a 9x13 baking dish with cooking spray; if you're baking it now without chilling, preheat the oven to 350° F.
In a small mixing bowl, mix together the melted butter, maple syrup, brown sugar, and cinnamon.
Spread this mixture on the bottom of the greased baking dish.
Place 2 rows of brioche bread slices in the pan, sprinkling raisins and half of the pecans in between each slice.
Sprinkle the rest of the pecans on top.
In a separate mixing bowl whisk together the eggs, milk, maple syrup, vanilla extract, salt, cinnamon, and nutmeg.
Pour the egg mixture over the bread in the pan.
At this point, cover and chill the casserole overnight, or go ahead and bake it.
When you're ready to bake the casserole, cover the dish with aluminum foil, and bake it at 350° F for about 30 minutes. Then uncover and bake an additional 15 to 20 minutes.
Once the casserole is baked, it should be soft in the middle but slightly crispy on top. It should come to an internal temperature of 160° F with a meat thermometer.
Serve with a dusting of powdered sugar or a generous drizzle of real maple syrup.