The 33-year-old is currently the favourite to join the champions following Mark Webber's announcement that he will quit Formula 1 at the end of the season.
"Two years in a row we have closed the gap with Red Bull," Boullier told BBC Sport.
"He wants to know if we will keep going like that. We are in discussions about the technical package we'll have."
Toro Rosso's Daniel Ricciardo is also said to be a candidate for Red Bull.