Microwave photonic cancellation notch filters have been shown capable of achieving ultra-high suppressions independently from the strength of optical resonant filter they use, making them an attractive candidate for on-chip signal processing. Their operation, based on destructive interference in the electrical domain, requires precise control of the phase and amplitude of the optical modulation sidebands. To date, this was attainable only through the use of dual-parallel Mach-Zehnder modulators which suffer from bias drifts that prevent stable filter operation. Here we propose a new cancellation filter topology with ease of control and enhanced stability using a bias-free phase modulator and a reconfigurable optical processor as the modulation sidebands spectral shaper. We experimentally verify the long term stability of the novel filter topology through continuous real-time monitoring of the filter peak suppression over 24 hours.