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.

About 1,700 people were asked for their opinions on proposals which were unveiled in June.
They involved new housing, a business hub and expansion of Liverpool FC's stadium, creating up to 700 jobs.
Mayor Joe Anderson previously said it was "shameful" there had been years of delays to improving the area.
The plans, drawn up by a consortium made up of Liverpool City Council, housing providers and Liverpool FC, would also see the creation of a wide avenue through Stanley Park ending in a new public square.
About 250 new homes would be built, with 296 removed to make way, and a 100-bed hotel constructed.
Feedback from residents during a six-week community engagement project will now be considered as more detailed plans are drawn up.
They will be subject to consultation before planning applications are submitted next year.
Mr Anderson said: "People have given us invaluable information about the entire range of regeneration ideas and concepts which we unveiled.
"In the coming weeks we will use this information to refine our proposals and to undertake another listening and consultation exercise.
"We believe the plans are exciting and will deliver a massive improvement in quality of life for many thousands of people and be of major benefit to the city, not just Anfield."
Haiti's presidential and legislative run-off elections have been postponed, officials have said.
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More than 80% of people living and working in the Anfield area of Liverpool are backing plans for a £260m regeneration, according to a survey.