Make cake according to package directions, baking in two 9-inch round pans. Make sure to grease the pans well so that the cakes will come out easily! Let cakes cool completely before assembling the trifle.
To make the whipped cream filling, beat the cream cheese and sugar with an electric mixer until smooth (about 2 minutes). Add the vanilla and whipping cream and continue to mix for another 2-3 minutes.
To assemble the trifle, place one round cake in a trifle dish and place half of the whipping cream mixture on top. Add most of the blueberries (saving a few for the top). Place the other cake on top of the blueberries and then add the other half of the whipping cream mixture.
Refrigerate until ready to serve (you can make this up to 24 hours in advance) and then top with raspberries, strawberries and remaining blueberries right before serving. Enjoy!