Prepare the oven: Preheat the oven to 350°F (175°C). Line a 9x5-inch loaf pan with parchment paper.
Cream the butter and sugar: In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl using a hand mixer), beat the melted butter and cane sugar until smooth and well combined.
Add the wet ingredients: Mix in the eggs and maple syrup until fully incorporated. Add the pumpkin purée, vanilla extract, and sourdough discard, then beat until smooth.
Combine the dry ingredients: In a separate bowl, whisk together the flour, baking powder, baking soda, pumpkin pie spice, cinnamon, and salt.
Mix the batter: Gradually add the dry ingredients to the wet ingredients, mixing just until no dry streaks remain. Be careful not to overmix, as this can make the bread dense.
Fill the loaf pan: Pour the batter into the prepared loaf pan and spread it into an even layer.
Prepare the cinnamon sugar topping: In a small bowl, stir together the cane sugar and ground cinnamon until well combined. After pouring the batter into the prepared loaf pan, sprinkle the cinnamon sugar evenly over the top of the batter before baking.
Bake the bread: Bake for 50–60 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs attached. If the top begins to brown too quickly, loosely tent the loaf with aluminum foil during the last 10–15 minutes of baking.
Cool before slicing: Allow the bread to cool in the pan for 10–15 minutes, then use the parchment paper to lift it onto a wire rack to cool completely before slicing.