Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper.
Cut the tops from the pumpkins and set aside. Hollow out the centers of each pumpkin and place the pumpkins onto one of the prepared baking sheets. Prepare the cake mix according to the package instructions, stirring in 1/4 cup of the pumpkin seeds at the end. Pour some cake batter into each pumpkin, filling halfway. Sprinkle the top of each with the remaining 1/4 cup pumpkin seeds.
Lightly brush the cut side of each pumpkin top with vegetable oil and sprinkle with sugar. Place the pumpkin tops cut-side down on the other baking sheet.
Put both baking sheets in the oven. Bake the pumpkin tops for about 25 minutes, and then set aside to cool. Bake the batter-filled pumpkins until a wooden toothpick inserted in the centers comes out clean, about 1 hour. Cool completely on a cooling rack.
Put a pumpkin top on each pumpkin cake and serve with maple syrup.