Who will be France's next president: A pro-European open to reform or Madame Frexit? It will be a "course-changing decision two weeks from now," Evelyne Gebhardt, vice president of the European Parliament, told DW. "Solidarity and fairness or nationalism and division."

Which one of these will win out depends on the result on May 7. A President Emmanuel Macron will carry European integration forward. Under Marine Le Pen, France would likely distance itself from its neighbors, double down on borders and get rid of the euro. Such a political earthquake could rattle the EU far more than Brexit.

Cautious optimism

European Commission President Jean-Claude Juncker and his colleagues were celebrating Sunday night. Macron winning the most votes was a sigh of relief for European leaders. "The much-anticipated domino effect following the Brexit vote and Donald Trump's election has not, so far, materialized. And the European project has won," Britain's Guardian newspaper wrote the day after the vote. "At least for now."

With Le Pen, a strong anti-European remains in the running for president. She came away from the first round of voting with 21.4 percent of the vote – 7.6 million French voters chose the populism of her party, Front National. Jean-Luc Melenchon, another anti-EU candidate, received 19.6 percent. As a far-left candidate, he had called first for EU reform, but getting out should that fail. He has yet to endorse either Macron or Le Pen.

"The election isn't over," said Pierre Moscovici, the European Finance Commissioner, though he doubts Le Pen's chances of winning the runoff. "However, I fear she'll get 40 percent." Should his prognosis come true, Macron would govern a country in which a sizable minority reject his pro-EU stance.

Diverging visions

Daniel Gros, director of the Centre for European Policy Studies in Brussels, is skeptical that Macron's party, En Marche!, can win a solid majority in June's parliamentary elections.

"It's important for Brussels that leaders at the national level have a definitive mandate," he told DW. "That is unlikely to be the case here."

Macron's financial policy interests also run counter to those of other EU members, in particular Germany. "I don't think he can make much headway at the European level."

Among other proposals made during the campaign, Macron has called for a common budget for the Eurozone. That would be hard for fiscally cautious leaders in Berlin to swallow. German Finance Minister Wolfgang Schäuble has made that much clear over many years.

European Parliament's Gebhardt, a member of the Social Democrats, believes Macron's financial policy is too liberal.

"There are positions I definitely cannot be part of," she said, but agrees with him that "we must rethink austerity measures. In southern European countries, they have contributed to rising unemployment and shrinking economies," leading to the rise of extreme parties.

Sensible EU policy

"The EU needs to make financial sense, of course," Gros said, but believes security is the largest issue that boosts populism. "The EU has to focus on security from within and without. That is where the biggest shortcomings are," he added.

That the French presidential runoff is a date with destiny for the EU is good, Gros said – and a risk for Macron, who has tied his fate to the EU. With the European question front and center, the election will serve as a definitive statement about France's commitment to a common Europe.