Preheat the waffle iron.Whisk together the flours, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice in a large bowl. Set aside.In a medium bowl, whisk together the milk, yogurt, eggs, canola oil, and maple syrup until well combined. Add in the sweet potato puree and whisk until incorporated.Pour the wet ingredients into the dry ingredients and stir until just combined, being careful not to over mix.Spray the waffle iron with cooking spray, and cook the waffles according to manufacturer's instructions.Top the waffles with pure maple syrup and toasted pecans, if desired. Serve and enjoy!