The duel comes a day after Sarkozy staged a huge rally to rival France's traditional May Day show of force by the left and after National Front leader Marine Le Pen scornfully rejected his bid to woo her far-right supporters.
The president is expected to use the debate to portray his front-running rival as a dangerous left-winger whose tax-and-spend policies signal a return to 1970s socialism that will doom the already struggling French economy.
Sarkozy is generally seen as a better debater than Hollande but few expect him to be able to reverse the opinion polls that forecast the Socialist will clinch Sunday's second round vote by around 54 percent to his 46.
Hollande will speak first in the debate to be broadcast live by several channels at 1900 GMT and which has been meticulously prepared – even down to the temperature of the studio – by media advisors of both candidates.
Hollande on Wednesday received advice from his former partner and mother of his four children, Ségolène Royal, who took on Sarkozy in 2007 when she was the Socialist candidate, in an election her right-wing opponent went on to win.
"The issue is not to let him (Sarkozy) escape his track record, because democracy is about knowing if one sticks to one's commitments. He must not be able to sidestep his track record," she told RTL radio.
Hollande must "above all remain himself" and must "keep this debate on an elevated plane even if (Sarkozy) tries to drag him down," she said.
Sarkozy's UMP party was meanwhile engaged in debate about how far it should engage with Le Pen, who got the support of 6.4 million voters in the April 22 first round of the election.
Defence Minister Gerard Longuet on Tuesday shocked many in the party when he said that Le Pen, "unlike her father" Jean-Marie, the firebrand founder of the National Front, was "someone we can speak to".
But UMP secretary-general Jean-Francois Cope stated categorically Wednesday that there would "never be any electoral deal talks with the National Front or discussion or negotiations with the leaders of the National Front."
Sarkozy has tilted ever further to the right since the first round in a bid to woo Le Pen supporters, vowing to "defend the French way of life", drastically reduce immigration and secure France's borders.
France holds elections next month for the National Assembly, where the National Front currently has no presence.
Le Pen hopes her third-place, 18 percent score in the presidential first round will translate into parliamentary seats and turn the Front into a powerful opposition party.
France's BFM-TV news channel said Wednesday it had dropped Dominique Strauss-Kahn's journalist wife Anne Sinclair from election night coverage because the disgraced Socialist was once more in the media spotlight.
"The serenity was gone, what with the affair kicking off again this weekend," said BFM-TV's boss Guillaume Dubois after the publication over the weekend of his allegation that Sarkozy orchestrated his downfall.
The ex-International Monetary Fund boss had been favoured to win the vote until May last year, when he was arrested in New York and accused of sexually assaulting hotel maid Nafissatou Diallo.
The charges were later dropped but a New York judge has ruled that he should face a civil case brought by Diallo.