Sift flour, baking powder and baking soda in a medium mixing bowl; set aside.
Cream margarine in a large mixing bowl; add sugars, mixing well.
Add eggs, one at a time, beating well after each addition; mix flour mixture and sour cream alternately into sugar mixture.
Fold in sausage and blueberries; pour into an ungreased 13x9x2 baking pan.
Cover, refrigerate overnight. Bake at 350' for 35 to 40 minutes or until golden on top; serve warm with blueberry sauce.
For blueberry sauce combine sugar and cornstarch in a medium saucepan; add water and blueberries. Heat and stir over medium heat until thickened and bubbly; continue heating for 2 minutes. Remove from heat; stir in lemon juice. Cool slightly before serving.