Seed giant Monsanto Co.’s (MON.N) unwanted takeover bid with Switzerland’s Syngenta AG (SYNN.VX) would face strong resistance in Brazil should it go forward, farmers and lawyers said, a hurdle that could delay or force major concessions to the $45 billion deal. Much of the public focus on the move has revolved around potential antitrust questions in the United States and the European Union, but challenges could also likely arise from emerging agricultural powers such as Brazil and China.