Bayer Leverkusen going for another unbeatable season record isn't going to be an easy one but their chances of lifting the trophy back to back is still on the high side with Xabi Alonso still as their manager. Especially now that Bayern Munich who the very team have a tight competition with them has a new manager in place which I don't see the possibility of Bayer Munich up this season.
Maintaining last season's unbeaten record is more difficult than achieving it, I don't think Leverkusen will finish the season unbeaten again this season because the competition will always be different every season. If they want to retain the trophy they successfully won last season, it is very realistic, currently Leverkusen has the best squad and is led by a coach who has the ability to bring out the full abilities of the players.
Bayern Munich is still Leverkusen's toughest competitor this season, last season's failure has made Munich very motivated to win the trophy again. Other teams also cannot be underestimated, Stuttgart, Leipzig and Dortmund also have the ability to provide surprises like Leverkusen did last season.