The editors from Gamestar (german PC gaming magazine and website) wrote in their last Preview, that savegames from the Witcher 2 can be imported. They did not state how, but I reckon it will be equivalent to the savegame Import in the Witcher 2.
The whole paragraph (with a slight spoiler) goes something like this:
Savegame-Import
While Console Players will not be able to inport their savegames from The Witcher 2, PC gamers can easily do this, preserving their story decisions from both(!) prequels. If you don't have a savegame any more or play on PS4 or Xbox One, there is an alternative.
At the end of the prologue, Gerald has to sit through a barber session to be presantable to the Emperor of Nilfgaard. During that, he can tell the barber about his past adventures, thus creating the decicions from the prequels - an elegant solution.
For those of you who can read german or are disgusted by my poor attempts at this translation, here is the full paper (the Import-part is the second "info-Box" on the first page.
http://www.gamestar.de/spiele/the-witcher-3-wild-hunt/artikel/the_witcher_3_wild_hunt,49062,3082308.html P.S. Again, for those fluent in german, try the Angespielt-Video, it's quite entertaining.