The race is wide open in CT for 2018. Here's some background on the potential candidates, roughly in order of likelihood of running.
Democrats:Dan Drew - Middletown Mayor, ambitious guy but pretty young (36), would have fundraising troubles
Kevin Lembo - Comptroller, wants to run but would probably defer to Wyman
Martin Looney - CT Sen Pres Pro Tem, interested but would defer to Wyman
Dan Esty - Yale Professor and Environmental Lawyer, husband to Rep. Elizabeth Esty (CT-5)
Susan Bysiewicz - Fmr SoS, well known but has a losing streak, out of politics too long
Ted Kennedy Jr - State Sen., has a famous name, some history of campaign funding issues
Jonathan Harris - Consumer Protection Admin, has been making the rounds, but pretty unknown
Nancy Wyman - Lt. Gov, may be too connected to Malloy
Dan Malloy - Incumbent Gov, he's probably out and would face a primary challenger if he ran
George Jepsen - CT AG, like's being AG and probably won't run
From what I've heard from state party people, Dan Drew and Kevin Lembo both really want the job and will run if Nancy Wyman does not. Right now, I would guess that both Malloy and Wyman pass, and the top tier of entering candidates will be Drew, Lembo, and Looney (with Lembo possibly a slight favorite).
Republicans:Prasad Srinivasan - State Rep., only declared candidate of either party so far
Tim Herbst - Trumbull First Selectman, mentioned by CT GOP Chair as a potential candidate
Peter Lumaj - Attorney, ran for Senate in 2012, created exploratory committee
Mark Lauretti - Shelton Mayor, mentioned by CT GOP Chair as a potential candidate
Tony Hwang - State Sen., created exploratory committee 2 years ago but internal #s are meh
Mark Boughton - Danbury Mayor, ran for Lt. Gov in 2010 and Gov in 2014, created exploratory committee
Rob Kane - State Sen., created exploratory committee
Erin Stewart - Not ruling it out, she's like the Republican version of Dan Drew, there's a post about her made earlier.
Greg Butler - Like's being considered a potential candidate
Len Fasano - Like's being considered a potential candidate
Toni Boucher - Linda McMahon said to watch her
Jayme Stevenson - Linda McMahon said to watch her
John McKinney - Fmr House Minority Leader, ran for Gov in 2014
Tom Foley - Gov nominee in 2010 and 2014, probably not interested in running again
I don't know as much about GOP politics in CT, but the bigger names to watch here are probably Herbst, Boughton, and Hwang.
This likely won't be accurate, but my very early guess is that Lembo defeats Herbst.
http://www.dailyructions.com/eye-on-estys-its-him-not-her-malloy-ally-testing-waters-for-2018-run-for-governor/https://dennishouse.tv/2017/01/02/who-will-run-for-governor-in-2018/