Charge and energy transfer are fundamental processes in van der Waals heterostructures (vdWHs), and controlling the transfer pathway is crucial for applications spanning from photodetection to photoluminescence. However, deterministic modulation of energy transfer (ET) and charge transfer (CT) is limited by static band alignments and physical barrier thicknesses. Here, we integrate an optical microcavity with two-dimensional (2D) heterostructures, leveraging the cavity resonance as a switch to convert the dominant mechanism from energy transfer to charge transfer, an unexpected transition that is tunable via laser parameters and cavity geometry. We reveal that the cavity-modified local electromagnetic environment thermodynamically stabilizes the CT pathways via dipole-selective coupling. Furthermore, cavity-mediated exciton-photon hybridization generates intermediate states that reconstruct the non-equilibrium relaxation landscape, while the cavity-enhanced local field induces photon-assisted tunneling to overcome intrinsic barrier limitations. Our work provides unprecedented flexibility for manipulating carrier dynamics in tunable optoelectronics, opening new avenues for ultrafast photodetectors, low-power photovoltaics, tunable switches, and various interdisciplinary applications.