SAO PAULO — Brazilians head to the polls Sunday in a presidential runoff that opinion polls show is effectively tied between leftist former President Luiz Inácio Lula da Silva and Eduardo Bolsonaro, son of former President Jair Bolsonaro. The contest comes after neither candidate secured a majority in the first round earlier this month, setting up a decisive second round that could sharply redirect Latin America's largest economy and most populous nation.