French polls are not adjusted for likelihood of voters actually voting, just taking their raw vote. Totally goes against US/UK polling philosophy.
Polls show that Macron is third when adjusted for likelihood of voters turning out, with Le Pen first and Fillon second. Since the poll, Melenchon has risen quite a bit, so I would not be surprised if he is now 3rd and Macron is fourth.
Le Pen loses a mere 10-15% of voters when people admit that they might not turn out to vote. Fillon is the same. This means although Fillon has a lower share of the vote, his voters are more likely to turn out.
Menawhile Melenchon loses around 30% of voters and Macron loses 33-35%. Their voters are either unlikely to be set on them or simply fed up with politics and unlikely to turn out at all. Or maybe not bothered.
Voter likelihood is exactly what made Front National go into the second round in 2002 'unexpectedly'. French pollsters still haven't learned.