Combine first 3 ingredients in a small, heavy saucepan over medium heat. Cook 5 minutes or until bubbly and sugar dissolves, stirring constantly. Pour sugar mixture into bottom of a 13 x 9-inch baking dish coated with cooking spray. Spread mixture evenly over bottom of pan. Set aside; cool completely.
Combine milk and next 5 ingredients (through eggs) in a large shallow bowl; stir with a whisk. Dip 1 bread slice in milk mixture; arrange bread slice over sugar mixture in dish. Repeat procedure with remaining 5 bread slices. Pour any remaining egg mixture over bread slices. Cover and refrigerate overnight.
Preheat oven to 350°.
Bake at 350° for 30 minutes or until lightly browned.
While casserole bakes, combine whipped topping and Grand Marnier. Place 1 bread slice, caramel side up, on each of 6 plates; top each serving with 1 tablespoon topping and 1 teaspoon pecans.