A conservative supermarket magnate was favored to win presidential elections Sunday that will determine who oversees expansion of the Panama Canal, the nation's economic engine. Ricardo Martinelli, of the opposition Alliance for Change, had a double-digit lead in the polls over former Housing Minister Balbina Herrera of Panama's governing coalition, which is led by the Democratic Revolutionary Party. The winner, whose term ends in 2014, will have to guide Panama through the world economic crisis and the $5.25 billion expansion of the canal to increase its capacity and accommodate larger ships. Few problems were reported despite heavy turnout at the country's 2,382 voting stations, observers from the Organization of American States said in a preliminary report issued after polls closed. Early returns were expected late Sunday.