The plot is possibly the most significant distinction between Witcher 3 and The Witcher TV show. The first two novels throughout the eight-part Witcher show, "The Last Wish" and "Sword of Destiny," by Andrzej Sapkowski, are the inspiration for the television series. Before continuing their joint exploits, it starts by introducing us to Geralt, Yennefer, and Ciri.
But on the other hand, the events in the books occur after several years in the game. In that regard, Witcher 3 isn't canon or focused on any one Witcher book but instead draws upon the themes and characters already established in the books to create its narrative. The clearest example of this is The Wild Hunt; in the novels.