Dortmund always does the same thing every season, which is where they will focus on one competition, after seeing their chances in the Bundesliga, I think Dortmund only has the chance to play more optimally in the Champions League. It is very unfortunate because in the Bundesliga this season's decline is quite severe, and Sporting chances are much greater to win the match.
On the other hand, the play-off round presents Brest vs PSG, a match that is no less interesting. At least this match is an opener to watch before the special match between Man City and Madrid.
The unique thing about Dortmund is that when they start to focus on one competition then usually their strength will start to increase rapidly. Last season Dortmund managed to produce good results both in the Bundesliga and in the UCL. But this season Dortmund doesn't seem to have good results in the Bundesliga. Even last week we also saw Dortmund lose to VfB in the Bundesliga. So it would be very natural if many would doubt Dortmund in the end. It's just that in the UCL we know that last season many people underestimated Dortmund. But they managed to surprise everyone by making it to the finals. And it's possible that this season the same thing will happen. But the chances will be quite small. And I think fighting Sporting CP will indeed be very difficult.
For the PSG vs Brest match, I think the result will be very clear, namely that PSG will most likely win the match, just like in their last meeting in Ligue 1 where PSG managed to beat Brest with a fairly landslide score.