Everton are reportedly offering the best salary, giving David Moyes' side an edge, while Marseille are said to only be prepared to pay 11million euros.
But the player's lawyer, Ralph Isenegger, has told French media M'Bia would prefer to play for Didier Deschamps' team in the Champions League.
Isenegger said: "We are in talks. It is a draw between Marseille and Everton so far.
"Stephane had a new phone call with Didier Deschamps on Sunday. They have very good first feelings. Didier has chosen him because he is aware he is the best Ligue 1 player in his position.
"Stephane would love to work with him, even if David Moyes is an excellent coach too.
"So it remains open. If Marseille makes a small additional effort, he will sign there. Otherwise he will move to England."