Preheat oven to 325 degrees. Coat bundt pan liberally with non-stick cooking spray. Set aside.
In large bowl, whip oil, sugar, vanilla, maple extract, eggs together until combined.
In small bowl, whisk together sour cream, milk and maple syrup. In a separate bowl, sift flour, baking powder, baking soda and salt together.
With mixer on low, alternate milk mixture with dry ingredients until everything is just incorporated. Scrape sides and bottom of bowl and mix briefly to ensure batter is evenly mixed.
Batter should be completely smooth. (A few small lumps is ok.)
Pour batter into prepared bundt pan, level the top and bake 55 min-1 hour 5 minutes or until toothpick comes out clean after being inserted.
Remove from oven and cool in the pan 15 minutes. Carefully remove cake from cooling rack and place onto cake stand.
For the icing, whisk powdered sugar, maple extract and heavy cream together until thick and smooth.
Drizzle over top of cake and down the sides. Top with chopped walnuts. Serve.