RoyalChicagoFC If the Champions League final is on the Saturday from 1945 (and assuming it's all over a bank holiday weekend), then...
--Schedule the play-off finals to go League 2 on Saturday, League 1 on Sunday and League Championship on Monday
--Play the League 2 game on Saturday at the Emirates, where the two sets of supporters might conspire to fill two-thirds of the seating capacity if the weather's nice
You could have the League 2 final kick off at noon on Saturday so to reduce overlap with the UCL final
You also could bump the League 1 final to 5:15 on Sunday afternoon so to give Champions League visitors plenty of time to head off and incoming supporters almost the entire day to make their way in
Of course, I'm of no doubt that there are plenty of perfectly awful reasons why this neither can nor will happen
Main reason it wouldn't happen is that the stadium is decorated as per the CL insignia for the final - teams need to train on the pitch etc etc...