Fernando Madeira comes to his new job as head of online business for Wal-Mart Stores Inc with a reputation as an e-commerce whiz, having engineered a surge in the retailer’s online sales in Latin America. In his enlarged role, the Brazilian company veteran will face a more formidable challenge – taking on Amazon.com Inc in the far-more developed U.S. online marketplace, where the world’s biggest retailer is yet to make its mark. Wal-Mart announced Madeira’s promotion on Monday, two days after unveiling plans to integrate e-commerce with its sprawling network of brick-and-mortar stores. Madeira’s job, from next week, is to make that strategy work.