QUITO—Ecuadorean leader Rafael Correa, a soccer-playing U.S. university student-turned-guayabera-wearing populist, is poised for an easy victory in Sunday's presidential elections—a win that would increase his grip on power and position him as a potential successor to Venezuela's ailing Hugo Chávez as Washington's gadfly in Latin America.

Most polls show Mr. Correa with a 40-percentage-point lead over of his main rival, Guillermo Lasso, a former banker who has promised lower taxes in this small oil-producing nation.

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