PARIS - Advertising agency Havas is aiming for organic revenue growth of about 5 percent this year, fueled by strong demand in the United States and Latin America, Chief Executive Yannick Bollore said on Wednesday. The world’s fifth-largest advertising holding company, which is majority owned by French tycoon Vincent Bollore’s eponymous group, also believes it can pick up new business this year as an unprecedented $27 billion in media buying and planning contracts come up for review in the U.S. The CEO said that Havas was in a good position since it only had to defend one contract, namely that of retailer Sears , which is expected to be decided by the autumn. It is also pitching for an $18 billion contract with food maker General Mills. “We are challengers rather than incumbents, so this spate of reviews is more of an opportunity than a risk,” Bollore said in an interview at the Cannes Lions advertising conference.