This is a question that comes up every time we work on a new play: who would play which role in a Muppet version?
This is especially tricky for this play - it doesn’t have much comic relief (except for right at the beginning, with the cobbler, which, being right at the start, isn’t really comic relief so much as a comic intro). Also, nearly every character is a dignified Roman statesman. Sam the Eagle is the only logical choice for pretty much every character except for the soothsayer (Gonzo, Fozzie and Bunsen Honeydew could all work here). Maybe they could have Wade and Wanda, the old-school singers from season one of The Muppet Show, as Caesar and Calpurnia. Piggy as Portia seems obvious, but it would sure work - she has the same mix of strength and apparent mental instability as Portia.
If we were hired to write the script for A Muppet Julius Caesar, we wouldn’t have much of the actual play in it. We’d do a big backstage story in which Sam the Eagle is trying to mount a very serious production of this immortal play, and, for some reason, thought that Fozzie could be trusted to play the role of Brutus with all due gravity (he’ll try his hardest, but fail). Kermit will work hard to be a good Mark Antony, but Gonzo, who is to be Caesar (Romans thought a big, hooked nose was a sign of esteem), feels that the play is missing something and rewrites it to include a lot more special effects, dancing chickens, spectacular stunts.
As Caeser, he’ll miraculously survive being stabbed twenty-three times (while whistling a medley of hits from A Funny Thing Happened on the Way to the Forum) (ta-da!), and the play would go downhill from there, presumably ending with a big song and dance number (we suggest Billy Joel’s “When in Rome”) that includes enough pyrotechnics to blow up the theatre. Hail Caesar!