Heat the oven to 350°F (175°C). Grease the loaf pan and add a parchment sling, keeping paper clear of the heating elements.
Whisk flour, baking soda, baking powder, salt, and pumpkin spice until evenly mixed. Combine topping sugar and cinnamon separately.
In another bowl whisk both batter sugars, eggs, pumpkin puree, oil, milk, and vanilla until smooth. Use plain pumpkin rather than sweetened pie filling.
Fold the dry mixture into the wet base, scraping the bottom of the bowl. Stop as soon as no dry flour remains.
Pour into the prepared pan and level the surface. Scatter the separate cinnamon sugar evenly over the top without stirring it into the batter.
Bake 55–65 minutes, until a center skewer shows moist crumbs with no wet batter. Shield the sugary top with foil if it browns too quickly.
Cool in the pan for 15 minutes before lifting onto a rack. Allow about 1 hour more so the moist interior firms before slicing.
Use a serrated knife and avoid pressing heavily on the cinnamon crust. Wrap the remaining bread once completely cool, keeping the top from getting crushed.
