Here the odds,
Bayern is still the favorite for the champions followed by Leipzig in 2nd place and Dortmund in 3dr place.
Here is the match schedule of the quarter-final,
Frankfurt vs Union (4/4),
Bayern vs Freiburg (5/4),
Numberg vs VfB (5/4),
and Leipzig vs Dortmund (5/4).
And, I agree, it's not impossible, everything change can happen in football. but, even though both teams seem strong on Bundesliga. we can't still ignore Munchen and Dortmund. I don't dare yet to bet on Eintracht and Union if there is no schedule yet on who meets who in the next round.
but if you still want to play, bet in under $1 is good for union.