In this work we address the problem of opportunistic allocation of downlink channels for the device to device (D2D) users. Because of the high interference in the downlink channel, D2D communication is usually studied in the context of uplink transmission in the literature. However, interference cancellation can be used in order to make D2D communication feasible in the downlink. It is seen that our proposed opportunistic method results in significant performance increase with respect to methods that purely with and without interference cancellation. As a practical scenario we consider the case that the D2D-Cellular User channel is not known and show that the proposed method still brings significant throughput improvement.