Prepare and bake cake, according to package directions, using two 9-inch round cake pans. Make sure to grease pans very well so cakes can be removed easily. Let cakes cool completely.
Beat cream cheese and sugar together in a large bowl with an electric hand mixer. Add vanilla and whipping cream. Continue to beat until thickened, creamy and combined.
Place one cake layer into the bottom of a large trifle dish. Spread half of the cream cheese filling over cake. Top cake with blueberries in a single layer.
Place second cake over blueberries. Spread the remaining cream cheese frosting over cake. Top with strawberry halves and a few more blueberries. Cover and chill trifle in fridge until ready to serve.