The Hubble constant tension between the value derived by Riess et al. (2016,2018) on the basis of Classical Cepheids distances and the Cosmic Microwave Background results is one of the most debated issues in current astrophysical literature. On the basis of an updated and extended set of nonlinear convective pulsation models, we are theoretically investigating the systematic effects on the Cepheid based extragalactic distance scale and the resulting Hubble constant. The predicted light curves and pulsation relations for both Galactic and Magellanic Cepheids, based on these new model sets, are tested on Gaia Data Release 2 (DR2) results. We find evidence of a Gaia DR2 parallax offset, consistent with independent results in the literature, but a general good agreement with the distances predicted by our theoretical pulsation scenario. We discuss the implications of our results and future perspectives, while waiting for Gaia Data Release 3.