Haiti's run-off election comes two days after the exiled former president Jean-Bertrand Aristide returned to Haiti from South Africa.
Aristide said he calm back to work on his educational foundation, but there are worries his return could disrupt voting. Authorities barred his Fanmi Lavalas party from the runoff.
The vote ends a turbulent election season that sparked fraud charges and deadly violence after first round of voting in December.
The candidates face the tough job of rebuilding a nation ravaged by last year's earthquake that killed more than 200,000 people and left over a million homeless.
The island nation has been beset by poverty, unemployment and a deadly cholera epidemic.
Final results of the runoff are to be announced on 16 April.