Bayern vs. Dortmund in the Bundesliga and Bayern vs. Dortmund in the Champions League final are very different games. The atmosphere is different, the game plan is different, the feeling of the fans is different, the motivation of the players is different. I don't agree with that, the German final would be very interesting to watch.
I think Dortmund and Real Madrid will play the final. In the end I hope we will see a final won by Dortmund. Whether it's Bayern or Real, instead of teams with huge budgets, the beautiful side of football is Dortmund, they deserve this final and this trophy.
You are right, even though Bayern Munich and Dortmund have often met in the Bundesliga, if they were in the Champions League competition they would play a different performance because the competition is bigger and will be watched by people from all over Europe because this is the biggest competition in Europe so every club will perform as fully as possible using all their strength with a stunning performance, even though Bayern Munich and Dortmund are used to being in the Bundesliga and Bayern Munich's level is still above Dortmund's, but when it comes to the Champions League, Dortmund will be a quite scary club and Bayern Munich should be wary of it. Dortmund cannot be underestimated. Dortmund's motivation in the Champions League is very strong, even though Dortmund's performance in the Bundesliga was less than optimal.
Yes, it looks like Real Madrid and Dortmund will advance to the final, between them they deserve the title if they are able to survive until the end, but my prediction is that Dortmund will be beaten by Real Madrid, who have a greater chance of winning the Champions League title thanks to their experience. But the surprise indeed that no one knows maybe if Real Madrid makes a mistake or gets a red card, Dortmund can take advantage of that opportunity, but I think it's unlikely that Dortmund can win the Champions League title and beat Real Madrid.