Spray three 9-inch cake pans with nonstick spray.
Combine sugar, oil, and eggs in a stand mixer until well blended.
Mix flour, baking soda, baking powder, salt, and cinnamon in a bowl.
Add the flour mixture to the sugar mixture and mix well.
Gently fold in shredded carrots and pecans.
Divide the batter among the pans and bake for 25-30 minutes.
Let the cakes cool completely.
Beat butter and cream cheese in a stand mixer.
Gradually add powdered sugar and vanilla until smooth.
Remove the domes from the cakes and set aside.
Place the first cake layer on a 10-inch cake board.
Frost the first layer and add the second layer.
Continue layering and frosting until all layers are stacked.
Frost the entire cake and coat the sides with chopped pecans.