The Witcher 3: Wild Hunt will allow you to carry over the decisions you made from the previous game. Unlike Mass Effect 3, which allowed you to import your previous saves, or Dragon Age: Inquisition, which used something called the Dragon Age Keep that let players customize their history, carrying over the choices you made in The Witcher 2 will be done via an in-game set of questions and answers.
Given that previous games in the series were not available on platforms apart from the PC, it should come as no surprise that the developers at CD Projekt Red opted to use this method of story importing.