Grease a 9x13-inch baking dish with butter and spread the cubed brioche bread evenly inside.
In a large bowl, whisk together the eggs, milk, half-and-half, pumpkin puree, brown sugar, maple syrup, vanilla, pumpkin pie spice, and cinnamon until smooth.
Pour the pumpkin custard evenly over the bread cubes and press gently so all pieces are soaked. Rest for 20 minutes (or cover and chill overnight).
Mix flour, brown sugar, cinnamon, and pecans in a small bowl; cut in the cold butter until crumbly and scatter over the casserole.
Bake uncovered at 350°F (175°C) for 35-40 minutes until golden brown and set in the center. Serve warm with maple syrup!