I am hoping someone with a more informed opinion will come along.
I understand that France has a system in which presidential candidates are whittled down in the first round of voting, to these 2 that remain. Le Pen is far right but most of the candidates in the preliminaries were much more moderate. The chances are that people who would have voted for other moderate candidates will switch to Macron.
Macron is a 39 year old former banker who formed a new political organisation, "En marche" only a year ago. He is standing as an independent but is a former PS (socialist party) member, and held senior roles with them.
France has been a prime target for terrorist attacks, it may well be that right wing attitudes in turn might have been fostered by this, hence the support for Le Pen. If Le Pen were to get in, she might well want to take France out of the EU as well.
Hence, other middle ground EU politicians are likely to be supporting a Macron win.
Just like this time last year, there is Too Much Politics at the moment.