Impossible to predict who will win
The draw is fairly balanced I would say and a lot of players have a really good shot at the title.
Going by previous results in Paris, Halep would be the logical choice for the favorite, however her results on clay (and in general) this year have been underwhelming. Still, she is a lock for QF and that match against Kvitova might just decide the winner.
Osaka has been flying under the radar, but she's actually had solid runs on clay
She will be a completely different player now that she is playing a Grand Slam and after melbourne I vowed never to underestimate her again
Another strong contender is obviously Pliskova who reached the AO SF, Miami final, won two titles including Rome and reached a SF here two years ago, losing in 3 sets to Halep. As the second seed, she has a very soft draw, so it remains to be seen whether or not her nerves will get the best of her yet again.
In my opinion, Kvitova is the #1 favorite, although just slightly. She has been incredibly consistent this year across all the events she has played and it's very evident that she cares very much about reaching the #1 ranking. In addition to that, an interesting fact is that the Australian Open runner-up has somewhat of a history of winning the French Open (2006 Henin, 2008 Ivanovic, 2011 Li, 2012 Sharapova, 2018 Halep and Safina and Serena almost did it in 2009 and 2016).