I feel they're still the favorites, although St. Etienne was one of the better away teams in Ligue 2 and Metz had only 3 home wins in regular season of Ligue 1.
They just have to win at home - if you want to remain in the top tier it should be the minimum you are able to do.

St. Etienne is one of the most decorated French clubs, so from a neutral standpoint' I'd rather have them there.