Rinse grapes and set aside in a colander to drain. Using a mixer, cream together the cream cheese, sour cream and powdered sugar until smooth. Add vanilla and beat in. Add grapes to a covered storage bowl and toss with the mixture. Beat heavy cream with powdered sugar and vanilla extract until thick and fluffy and doubled in volume. Fold the whipped topping into the cream cheese dressing. Cover and refrigerate overnight. Transfer to a large serving bowl, sprinkle the top liberally with brown sugar and pecans just before serving