In a small saucepan, sprinkle gelatin over cold water; let stand 1 minute. Add sugar; heat and stir over low heat until gelatin and sugar are completely dissolved. Transfer to a bowl; whisk in sour cream and vanilla. Refrigerate 10 minutes., Fold in whipped topping. Pour into a 4-cup mold coated with cooking spray. Refrigerate, covered, until firm, about 4 hours., For sauce, drain berries, reserving syrup. Add enough water to the syrup to measure 3/4 cup. In a small saucepan, mix cornstarch, sugar and syrup mixture until smooth. Bring to a boil; cook and stir until thickened, about 2 minutes. Cool slightly. Stir in drained berries; refrigerate until serving., To serve, unmold dessert onto a serving plate. Serve with sauce.