The French election is really complicated with four candidates still in the running going into first round voting. Please feel free to quibble, but for the USA audience I will note them as: (center-left) Macron at 56%, (far-right) Le Pen 19%, (center-right) Fillon at 19%, and (far-left) Melenchon 5%. Again, apologize for the crude labeling.
The French election has a very reasonable voting system, similar to Georgia Sixth House election: in the first round of voting (Sunday, April 23) if someone gets over 50 percent of the vote s/he wins, if not the top two candidate do a head-to-head run-off (Sunday, May 7). Of course, unlike the USA election, the voting is on Sunday to maximize ease of turnout and the run-off if two weeks later (rather than two months later), because the French are not masochistic.
Pollster’s running average for the first round: Macron 23.5%, Le Pen 22.0%, Fillon 20.0%, and Melenchon 19.4%. I have no insight into the quality of French polling, but (1) these polls have been way too stable (and I will grudging note that Nate Silver pointed this out on Twitter) which means we need to be concerned that they are herding or reporting results that conform to what everyone else is doing (2) everyone is pretty tight if you assume 4-5 pp as MOE.
Market probabilities for getting through first round: Macron v. Le Pen (55%), Macron v. Fillon (12%), or Macron v. Melenchon (3%). Markets have Macron at 70 percent to make it to the second round and very likely to win against any of the other three candidates. He is leading the polls and just needs to come in second. It gets much more interesting if Macron does not make through: Fillon v. Le Pen (18%), Melenchon v. Le Pen (10%), or Melenchon v. Fillon (3%). There is only a 3 percent chance that neither Macron or Le Pen make it through. Reasonable, as they are one and two in the polls. If Le Pen faces Fillon it is close match, Fillon is leading in head-to-head polls, but he is crippled with scandal. If Le Pen faces Melenchon it is very hard to judge, without new polling, where the mass of center-right and center-left voters will go. Melenchon certainty has a good chance.