I hope to see a different club in the finals if any of these two clubs did not make it to the finals. Next season is hard to predict with the current informations on ground. I want to see that different club apart from Real Madrid and City that will surprise the world just like what Dortmund did.
Nothing is impossible, we can see that Leverkusen is performing very well this season, they can even beat Dortmund in the domestic league, therefore Leverkusen will most likely maintain their consistency until they reach the UCL final next season, but still Manchester City and Madrid will to be one of the best who will enter the important rounds, especially the UCL final, I can't guess which one is the best. As you said, Dortmund came full of surprises as did Inter Milan in the season before they reached the final.
We might be able to see a successful team in the Bundesliga like Leverkusen qualify for the UCL final next season, I also think that Xabi Alonso certainly wants his team to reach a difficult level again after their failure in the UEL final yesterday because they were defeated by Atalanta of course they will perform better. good and learn from their mistakes, I think Leverkusen will be a threat to other teams in the UCL, however the competition will still be tight as to who is the best and can reach the final. but Madrid and Manchester City will still be in the UCL final next season.