Maxime Vachier-Lagrave, who very, very nearly qualified for the Candidates (by several different means) has written up his own preview of the event, singling out Fabiano Caruana and Levon Aronian as his favorites. (He's not alone in this, as he acknowledges; many others - and I'd include myself here - are of the same opinion.) He also offers some very high praise of Vladimir Kramnik:
In my opinion, Vlad is probably the player in the world who best understands chess. You can show him whatever position, his instincts will seldom let him down. He will always find what the evaluation of the position is and which plan to adopt.
A well-known Norwegian didn't care for this very much, expressing his disapproval on Twitter, and in Kramnik's and MVL's defense came Anish Giri. Giri has two dogs in the fight: first, he and Magnus Carlsen have been exchanging barbed tweets for years now; second, Giri is one of Kramnik's helpers for the Candidates. You can read more about how their little feud progressed at the preceding link; perhaps it has continued on their Twitter feeds in the meantime.
Returning to more buttoned-up preview material, Jan Gustafsson has a preview series of videos on Chess24, and Chess24 also has a series of articles on the Candidates. In order from the most to the least recent:
Shakhriyar Mamedyarov, Vladimir Kramnik, Levon Aronian, Alexander Grischuk, Fabiano Caruana, Ding Liren, Wesley So, and Sergei Karjakin.
Happy reading and viewing!