In a contest overshadowed by the election of Donald Trump in the United States, support for the early favourite Juppe has slipped and Francois Fillon, who served as prime minister under Sarkozy, has risen fast.
The right-wing nominating contest is crucial because with the French left divided, the winner is expected to go on to take the presidency in May, beating far-right leader Marine Le Pen in the runoff.
Juppe, 71, entered the two-month-long contest with polls showing him to be France's most popular politician, but his approach of playing the moderate against the fiery Sarkozy and the conservative Fillon appears to be backfiring.
Most polls now show Juppe and Sarkozy are neck-and-neck at around 30 percent, with Fillon close behind after making striking progress in recent weeks.
The two winners on Sunday will go through to the second round run-off a week later.
Two becomes three
“We were expecting a duel but in the end a three-way contest has emerged,” political scientist Jerome Jaffre said in Le Figaro newspaper on Thursday.
Many have noted that 62-year-old Fillon's rise had coincided with the publication of his latest book entitled “Beating Islamic totalitarianism”.
An often confused final TV debate of the seven candidates on Thursday offered few clues about the possible outcome, although viewers polled afterwards said Fillon had performed the strongest.
Sparks flew when Sarkozy was asked about fresh claims that he received millions in funding from the late Libyan leader Moamer Kadhafi towards his 2007 campaign.
Sarkozy called the question “disgraceful” and refused to answer.
Turning to the Trump effect, the former president said a more isolationist America created “a fantastic opportunity for France and Europe to re-establish a leadership role” on issues including border security and the reform of the UN Security Council.
“The next five years will mark the return of France and Europe to the international scene. America won't be there to put us in the shade,” he said.
Juppe meanwhile said the Trump-era heralded a triple “shock” — in the areas of trade, defence and the environment.
A return to protectionism would be “a tremendous regression”, Juppe said, while warning Europe against being “naive” in its dealings with the United States.
The three leading candidates have similar programmes, underpinned by pledges to reinforce domestic security in a country still under a state of emergency following a series of jihadist attacks.
They also share a desire to reinforce European borders and reduce immigration, while tax cuts also loom large.
The choice will come down to style.
Sarkozy has emphasised his tough-guy credentials, saying it makes him a better choice to handle Trump than the mild-mannered Juppe.
Fillon, who is popular in the business world, has promised “radical” economic measures but is the most conservative of the three on social issues.
Another unknown factor in Sunday's first round is the number of left-wing voters prepared to pay two euros and sign a declaration that they subscribe to “the values of the centre and the right” to vote in the right-wing primary.
Those who do are expected to vote against 61-year-old Sarkozy, who remains a highly divisive figure in France four years after he left office.
When the right-wing candidate is chosen on November 27, it is expected to trigger an announcement from deeply unpopular Socialist President Francois Hollande on whether he intends to bid for re-election.
On Wednesday, Hollande's former economy minister Emmanuel Macron announced he would stand as an independent.
by AFP's Guy Jackson