Opposition factions alleged fraud during the first round of voting and there have been widespread street protests.
A special commission set up by President Michel Martelly last week is to investigate the electoral process.
There were more violent protests on Saturday when the results for the legislative vote was announced.
Jovenel Moise, a banana exporter, won the most votes in the presidential elections but with 33% fell short of a majority.
He is to face ex-state construction company head Jude Celestin, who came second with 25%.
Mr Moise has little political experience but has the backing of current President Michel Martelly. Mr Celestin is seeking the presidency for a second time.
Whoever wins will face a daunting task when taking over from Mr Martelly in February. Haiti is the poorest nation in the Americas.
Since it was devastated by an earthquake in 2010, the country has relied largely on international donations and foreign aid from the United States and other countries.
Haiti's presidential and legislative run-off elections have been postponed, officials have said.