Earlier on Sunday, the under-pressure French conservative Francois Fillon apologised to his supporters for the fake jobs scandal that threatens to sink his presidential bid but said he was sure he would be proved innocent.
With many of his former allies shying away from Sunday's rally, Fillon's wife Penelope broke her silence over the allegations that she was paid around 850,000 euros of public money for work she never did. "If it hadn't been me, he would have paid someone else to do it, so we decided that it would be me", she said. "I said to him that he had to keep going to the end".
Mr Fillon urged thousands of supporters not to "give up the fight" at a central Paris rally backing his campaign on Sunday. It is unclear what Fillon is planning to say in the appearance on the France 2 channel. "I am not autistic", he said, "I want to convince my friends that my programme is the only one that can bring about recovery for the country".
It's after it was claimed in the French satirical magazine Le Canard Enchaine that Fillon's wife Penelope and other family members were paid nearly a million euros in public money to aid him in his politicial duties, but did not actually do the work they were paid for.
Juppe would have 26.5 percent of votes, narrowly ahead of Macron on 25 percent, while Le Pen would slip to third place on 24 percent, according to the Odoxa-Dentsu Consulting survey of 943 people.
Some senior lawmakers in his Republicans party have called for Fillon to be replaced immediately, with polls now suggesting he would be eliminated in the first round of the election on April 23. Instead, centrist candidate Emmanuel Macron is benefiting from a boost in the polls and is consolidating his position to win the election in a head-to-head against Front National candidate Marine Le Pen.
Fillon's chances for France's two-round April-May presidential election have fallen since the corruption allegations emerged.
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With some members of his party urging him to drop out, Sunday's rally on the Trocadero plaza opposite the Eiffel Tower - heavy rain is forecast - will be a test of how much confidence remains.
On Wednesday, Fillon revealed he would meet investigating magistrates on March 15 and be charged.
But Juppe, who is more centrist than Fillon, also has baggage - he was given a suspended jail sentence in 2004 over a party funding scandal.
Last Saturday, five Members of the European Parliament from the Republicans party called for another candidate to be appointed before the March 17 deadline.
If Fillon steps down and he is replaced by well-known Republican Alain Juppe, polls suggest Juppe would knock Le Pen out of the race.
Fillon was a surprise victor of the conservative nominating contest in November, campaigning as a "Mr Clean" unsullied by his opponents' legal difficulties and pledging to slash 500,000 civil servants' jobs.
Yet a poll on Friday showed Juppe would vault into the lead if he stood.