||We investigate the controllable generation of robust photon entanglement with a circuit cavity electromechanical system, consisting of two superconducting coplanar waveguide cavities capacitively coupled by a nanoscale mechanical resonator. We show that, with this electromechanical system, two-mode continuousvariable entanglement of cavity photons can be engineered deterministically either via coherent control on the dynamics of the system, or through a dissipative quantum-dynamical process. The first scheme, operating in the strong-coupling regime, explores the excitation of the cavity Bogoliubov modes and is insensitive to the initial thermal noise. The second one is based on the reservoir-engineering approach, which exploits the mechanical dissipation as a useful resource to perform ground-state cooling of two delocalized cavity Bogoliubov modes. The achieved amount of entanglement in both schemes is determined by the relative ratio of the effective electromechanical coupling strengths, which thus can be tuned and made much larger than that in previous studies.