Remake: Who should play Harold + Maude?
If there were a remake, I know, God forbid, but anyway, if there were, I think Sam Riley (Control, Franklyn) would make a great Harold, or Lukas Haas, though he's getting a bit old for the role imo.
As for Maude, Doris Day would guarantee 'shock' value. Otherwise, a makeup free Helen Mirren would do nicely imo.