Preheat oven to 350° and spray a large Bundt pan. Using a mixer with the paddle attachment, combine the softened margarine and sugar and mix until light and fluffy. Add the non-dairy milk, dairy-free sour cream and vanilla. Beat until well combined.
In a separate medium bowl, combine the flour, baking powder, baking soda and salt. Slowly add it the margarine mixture and beat well. The batter should be thick. Pour half the mixture into a prepared mixture and spread out.
Sprinkle the cinnamon filling over the batter. Add the remaining half of the batter and fully cover the filling. Bake for 40-45 minutes or until the tester comes out clean. Cool completely and turn over on a serving plate. Dust with confectioners' sugar.