Preheat the oven to 350°F (180º C). Line a 9x5-inch (23x13-cm) loaf tin with parchment paper and set aside.
In one bowl combine the flour, pumpkin pie spice, baking powder, and salt. Mix well and set aside.
In another bowl combine the pumpkin purée, eggs, sugars, oil, and vanilla. Mix together until smooth.
Add the flour mixture to the wet ingredients and stir to combine. Scoop one half of the batter into a separate bowl.
Combine the cocoa and milk in a small bowl and stir until the cocoa dissolves. Add the cocoa mixture to one of the bowls of pumpkin batter and stir until the chocolate batter is well mixed.
Alternate scooping the chocolate and pumpkin batter into the prepared loaf tin until both batters are in the tin.
Once all the batter is in the tin, run a butter knife through the batter in swirly figure 8's. Swirling with the knife is what creates the marble effect. Be sure the knife reaches the bottom of the pan for the marbling to be apparent throughout the whole loaf.
Bake the marble loaf cake for 60 to 70 minutes, or until the top springs back when lightly touched.
Cool on a wire rack for 10 minutes, then turn the loaf out onto the rack and cool it completely before icing with maple glaze.
Once the loaf has cooled, mix the powdered sugar and 1 teaspoon of the maple syrup.
Continue to add maple syrup by the ½ teaspoon until the glaze is thick but pourable.
Drizzle the maple glaze over the marble loaf cake, slice, and serve.