Preheat oven to 400 degrees. Line a large baking sheet with parchment paper; set aside.
To make the Cream Puffs: In a medium saucepan combine water, butter, sugar, and salt. Bring to boiling over medium heat. Add flour all at once, stirring vigorously with a wooden spoon. Cook and stir until mixture forms a ball and pulls away from the side of the pan. Remove from heat; cool for 10 minutes. Add eggs one at a time beating well with a wooden spoon after each addition.
Drop 8 heaping tablespoons of dough 2 inches apart onto the prepared baking sheet. Bake for 30 to 35 minutes or until golden brown and firm. Transfer cream puffs to a wire rack and let cool.
To make the Pumpkin Mousse Filling: using a chilled large mixing bowl beat 1 cup whipping cream, 3 tablespoons sugar, and 1 teaspoon pumpkin pie spice with the chilled beaters of an electric mixer on medium speed until soft peaks form (tips curl). Fold in 1 cup canned pumpkin. Cover and chill for up to 4 hours.
To make the Maple-Caramel sauce: In a small heavy saucepan stir together 1/2 cup packed brown sugar and 1 tablespoon cornstarch. Stir in 1/3 cup half-and-half or light cream, 1/4 cup water, 2 tablespoons pure maple syrup, and 1 tablespoon butter.
Cook and stir over medium heat until slightly thickened and bubbly (mixture may appear curdled before it bubbles). Cook and stir for 2 minutes more. Remove from heat; stir in 1/2 teaspoon vanilla.
Using a serrated knife, cut each cream puff in half horizontally; remove soft dough from inside. Fill cream puffs with Pumpkin Mousse. Replace tops. Spoon some of the warm Maple-Caramel Sauce onto eight dessert plates; sprinkle with some of the toasted pecans.
Place a filled cream puff on top of the sauce on each plate. Drizzle each cream puff with remaining sauce and sprinkle with remaining pecans. Cover and chill for up to 3 days or freeze for up to 3 months.