I dunno if Eugene Levy or Catherine O’Hara would be considered “too big” with Schitt’s Creek becoming so big in recent years.
Using Wikipedia as a source (I know), O'Hara and Short only overlapped for three episodes of
SCTV. Levy and Short did a bit over one year together.
I fear both of them are in the "we don't do game shows" category -- a quick glance at IMDB shows nothing at all for Levy, and just celebrity
Millionaire and a
Whose Line episode for O'Hara.
A shame neither Neil Patrick Harris or Jason Alexander seem to have been invited back.