Using transmission electron microscopy techniques, we identify the extended defects of interstitial and vacancy types found after H implantation and annealing in GaN. We statistically analyze the effect of boarding or sandwiching GaN between strained superlattices on these populations of defects. We finally demonstrate the possibility to use compressively strained layers to localize and favour the precipitation of vacancy type defects in GaN. The source of excess vacancies, the mechanism responsible for the cavity localization, and the drastic increase of their volume fraction are discussed.