I am very optimistic that he can win the Bundesliga trophy again, but he will have a hard time winning the UCL trophy. Xabi Alonso will try to do his best this season including bringing Leverkusen to compete with other elite clubs in the Champions League, but he will also prioritize the Bundesliga because he wants to win the trophy again in a row.
Bundesliga is also a major trophy like the champions league, so even if Xabi Alonso is able to win the Bundesliga again, it is a very great achievement for him again for the second season. The champions league trophy will not be an easy one for Xabi Alonso to win in the next season. You need experience and consistency in this game before you can be champions. Xabi Alonso can try for the first time and he might be lucky or will have to try again and again before he can find the best fit for the club to win the trophy. I just feel he can win the Bundesliga trophy easier than winning the champions league but trying is something he must have to do before he can be sure of his place in that competition.