Strain frozen berries over a bowl, reserve juice.
Whip cream with powder sugar and vanilla in large bowl and reserve half for topping. Combine other half with the mascarpone.
Line a 13 x 9 glass-baking dish with half of the pound cake pieces. Pour half of the juice over the pound cake. Spread half of the frozen raspberries on the pound cake and then spread one-half of the whip cream/mascarpone mixture over the raspberries. Repeat layering with the remaining pound cake, juice, raspberries, mascarpone mixture. Top with the reserved whip cream and fresh berries. Cover and refrigerate at least 3 hours or overnight.