Preheat oven to 350 ℉.
In a medium bowl, whisk together all-purpose flour, baking powder, baking soda and ground cinnamon. Set aside. Note: sift flour if necessary to remove any lumps.
In a separate bowl, combine maple syrup and sour cream in a small bowl and mix to combine. Set aside.
Place butter and brown sugar in the bowl of a stand-,mixer. Using the paddle attachment, mix together until light and creamy (2 - 3 minutes). Scrape bowl down as needed. Note - a hand-mixer may also be used.
Add eggs to bowl. Mix until well combined. Scrape bowl down as needed.
Add ⅓ of the flour mixture to bowl. Mix on low speed until just combined.
Add half of the maple syrup mixture to bowl. Mix on low speed until just combined.
Add another ⅓ of the flour mixture and mix until combined.
Add the remaining maple syrup mixture to the bowl. Mix on low speed until just combined.
Add the remaining flour mixture and mix until combined.
Spoon ½ of the cake batter into Bundt pan. Smooth with a rubber spatula. Use the back of a spoon to create a tunnel in the batter.
Add streusel filling into the tunnel you just created. Take care to keep the mixture away from sides of pan.
Add remaining cake batter to pan over streusel filling. Smooth gently with a rubber spatula.
Bake for 40 - 45 minutes at 350℉ or until top is quite brown and a toothpick inserted in the center comes out clean. Note: you may also check for doneness but inserting an instant read thermometer in middle of cake. Internal temperature should be 180℉.
Remove pan from oven and cool upright for 15 minutes.
Flip pan upside down onto a cooling rack and let cool completely. Lift pan off cake - it should release from pan on its own. If not, use a blunt knife and gently loosen sides.
While cake is cooling, bake remaining ¼ cup of pecan streusel for 8 minutes at 350℉. Set aside to cool.