Place canned cream cheese frosting in a large pastry bag fitted with a star tip. Insert the tip into the top of each of twelve 2-1/2-inch white cupcakes, squeezing about 2 teaspoons frosting into each. Pipe swirls of frosting onto tops of cupcakes. Arrange fresh blueberries and strawberry halves on cupcakes; store in the refrigerator. If desired, dust with powdered sugar just before serving.