Step 1: Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan or springform pan.
Step 2: Prepare the streusel by mixing 1/2 cup flour, 1/3 cup brown sugar, and cinnamon in a small bowl. Cut in the cold butter until the mixture resembles coarse crumbs. Chill in the fridge.
Step 3: In a large bowl, cream together the softened butter, granulated sugar, and 1/4 cup brown sugar until light and fluffy.
Step 4: Beat in the eggs one at a time, then stir in the maple syrup and vanilla extract.
Step 5: In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.
Step 6: Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream. Do not overmix.
Step 7: Gently fold in the diced pears using a spatula.
Step 8: Pour the batter into the prepared pan and sprinkle the chilled streusel evenly over the top.
Step 9: Bake for 45-55 minutes, or until a toothpick comes out clean. Let the maple pear cake with streusel topping cool for 15 minutes before serving.