We report on the realization and characterization of a silicon-based integrated optical platform which implements a vertical coupling scheme between a Whispering-gallery type microresonator and a buried dielectric waveguide. The vertical coupling allows for the separation of the resonator and the waveguide into different planes, which enables one to realize the optical components in different materials/thicknesses. The high optical quality of this cavity micro-optical system follows from the accurate planarization of the waveguide topography, which is achieved by multiple depositions-and- reflows of a borophosphosilicate glass over strip waveguides. Importantly, we demonstrate the feasibility of our approach for wafer-scale mass fabrication of freestanding planar resonators suspended in air and coupled to integrated bus waveguides. This opens the door for the realization of stable all-integrated resonator systems for optomechanical and metrological applications and has the potential to substitute today's complicated fiber-taper coupling schemes.