I would have said real Madrid will win them just like they did the last time but they currently have deprecating performance, may be because of injuries that has been affecting the players, however I no Borussia Dortmund to be a club that normally take the champions League matches very serious.
No, this is not an easy match for Real Madrid even though they are playing at home, what is clear in this match I conclude that the chances for Real Madrid to win it are still very small.
Moreover, what you said is also true if Dortmund always takes the UCL match very seriously and always appears impressively, look at the previous two match showing they managed to win and last season Dortmund managed to reach the final even though they were defeated by Real Madrid.
Only possibility that has big chance of happening is draw because each team has conditions with quite significant advantages and disadvantages, it will not be easy for Real Madrid to win and vice versa for Dortmund.