In March 2008, Cantelli joined the new Ultimate Signature team to contest the Formula Renault 3.5 Series. He took part in the first five races of the season with the team, but was replaced by Esteban Guerrieri after the Monaco round. After missing the following event at Silverstone, Cantelli returned to the series at the Hungaroring, replacing Aleix Alcaraz at Italian team RC Motorsport. He finished in the points on one occasion, at the Nürburgring, to claim 28th place in the final standings.
