My suggestion here is to chose the best stadium in the 128 teams competing in the cup to host the final match, whatever the owner's team is in the final or not just like what happens in the reality.
and to chose also the best stadium from the 32 teams competing in the champions league to host the final.
The best stadiums "in case if you like it" will be chosen according to stadium capacity, training ground, parking area and club shop.
hope you like my suggestion.