Heat oven to 400°F. In large bowl, whisk together flour, baking powder, 2 tablespoons of the cinnamon-sugar, baking soda and salt. Using a pastry blender, cut in shortening until mixture resembles coarse meal. (Alternately, dough can be made in a food processor, using on/off action so as not to overwork.)
Stir in buttermilk and maple syrup until all ingredients are moistened. Stir in pecans (dough will be soft). Turn out dough onto generously floured surface. With floured hands, pat dough to a 9-inch square. Cut out biscuits, using a 2-inch round fluted or straight-sided biscuit cutter. Gather scraps together and cut additional biscuits for a total of 24. Transfer all to an ungreased baking sheet.
Brush biscuit tops with 2 tablespoons milk. Sprinkle each biscuit with 1/8 teaspoon of the remaining cinnamon-sugar. Bake at 400°F for 12 to 15 minutes. Remove biscuits from oven and immediately transfer to a wire rack. Serve slightly warm.