Aside the advantages of playing on home turf and all, Nantes have been awful recently while Juventus seem to have gotten their form back and even have a shot at the league. To me, Juventus would win easily. In fact they'll win both legs of that tie. Nantes is no where near where Juventus is right now. If the match took place when Juventus where in a poor form then Nantes would have stood a chance but right now they're currently 15th on the league table. Their last win against Auxerre was their first win in 6 matches. I really don't see how their going to qualify ahead of Juventus in the Europa league.
Most chances Juventus will pass through this early test in the UEFA Europa Cup because they have enough quality for giving punishment's to team like Nantes which is already near the relegation zone in French Ligue 1 and Juventus form is amazing with seven matches winning streak and conceding no goal in these all matches mean they are doing more than expectations hopefully they could be considered this event as good priority because with this spirit they will be able to perform good and having positive result in this match and event.
Even at home any team can shock opponent but still for the team like Nantes could be the toughest job because their quality is not near the team like Juventus which is now third in the Serie A.