In a conventional slot waveguide structure, light is strongly confined in the slot region only either for the quasi-transverse electric (TE) (in a vertically oriented slot) or for the quasi-transverse magnetic (TM) (in a horizontally oriented slot) fundamental eigenmode, which enhances the optical forces, thus decreasing the optical power necessary to control the displacement of the device, but only for one eigenmode polarization at a time. In this work, we analyzed the optical forces in a cross-slot waveguide, which is formed by four suspended silicon waveguides separated by two orthogonal air slots. Cross-slot waveguides can strongly confine light in both quasi-TE and quasi-TM polarizations, thus enhancing the optical force and reducing the optical power for both. Our simulation results show that by adjusting the optical power and the light polarization, it is possible to control the displacement of the waveguides in the vertical or in the horizontal direction almost individually, or in both directions simultaneously. The proposed nano-optomechanical device has potential applications in active photonic devices and novel mechanisms for nanosensors and nanoactuators, such as optical nanogrippers and nanotweezers.