The 24-year-old Ivory Coast international has 19 caps and three goals. He arrived from Nice.
An agreement between the clubs has been reached, with only a few details still to be finalised.
Guessand has featured in 13 Premier League matches for the Villans, mostly on the right wing.
If confirmed, the switch should allow him to play more centrally, a role in which he is more comfortable. Palace were among the most persistent suitors last summer.