Dawn space mission will provide the first, detailed data of two of the major bodies in the Main Belt, Vesta and Ceres, and will allow us to study in depth the crater record on the surface of these asteroids and get an insight on their place in the context of Solar System history. In the framework of our studies on the origin of Solar System, we modelled the accretion of Jupiter and, through an N-Body code developed on purpose, we evaluated the flux of impactors on Vesta and Ceres keeping track of their formation zones. We also studied the effects of the possible inward migration of Jupiter on the rate and the characteristics of the impacts. We here describe the different scenarios and their implications for the evolution of Solar System to provide a reference frame for future studies of Vesta's and Ceres' cratering histories.