Overnight French Toast Casserole

1 cup packed light brown sugar
6 tablespoons butter, melted
1 cup pure maple syrup, divided
1 cup chopped toasted pecans, divided
12 1-inch-thick baguette slices from 1 baguette, ends discarded
5 large eggs, lightly beaten
1 1/4 cups whole milk
2 tablespoons granulated sugar
1 teaspoon orange zest plus 1 Tbsp. fresh juice
1/2 teaspoon ground cinnamon
1 1/4 teaspoons vanilla extract, divided
2 tablespoons bourbon
Powdered sugar, for serving

Stir together brown sugar, melted butter, and 1/4 cup of the maple syrup.
Spread mixture into a 13- x 9-inch baking dish lightly coated with cooking spray.
Sprinkle with 3/4 cup of the pecans.
Arrange baguette slices evenly on top.
Whisk together next 5 ingredients and 1 teaspoon of the vanilla.
Pour over baguette slices, cover, chill 8 hours.
Preheat oven to 350°F. Remove baking dish from refrigerator; let stand at room temperature 10 minutes.
Bake, uncovered, until golden brown and set, about 35 minutes.
During final 10 minutes of baking, combine bourbon and remaining maple syrup and vanilla in a saucepan.
Cook over low, stirring, until warm, 2 minutes.
Remove from heat, cover pan.
Sprinkle casserole with powdered sugar and remaining 1/4 cup pecans.
Serve with Bourbon-Maple Syrup.