Mechanical transfer of GaN-based heterostructures using h-BN as the release layer [Y. Kobayashi, K. Kumakura, T. Akasaka, and T. Makimoto, Nature 484, 223 (2012)] has promising applications for the next-generation optoelectronic devices. We investigate such transfer mechanism by mapping out the interlayer sliding energy landscape at each interface of a model heterostructure composed of GaN/BN/substrate together with the reference case of BN/BN interlayer sliding. The calculated results based on density functional theory find a nearly free sliding path for BN/BN, while a slightly higher energy barrier is predicted for hetero-interfaces of strained GaN/BN and BN/graphene substrate. The unstrained GaN/BN interface facilitates an easier peel-off of GaN from the BNlayer. Thus, the sliding mechanism, which can also be described by the registry index model, shows dominance of the electrostatic interaction terms associated with the constituent layers of the system, though the van der Waals interaction term seems to determine the equilibrium interlayer distance for the systems considered.