Julius Caesar-
James Franco
because he is very cocky, and would probably make a stupid mistake in order to keep his reputation.
Brutus-Brendon Urie
...I just wanted to add him to the list. :)
Antony-James Marsden
Because he's always cracking jokes, but can also take on serious roles.
Calpurnia-Jennifer Love Hewitt
because she's good at playing the "worried wife".
Portia-Angelina Jolie
because she's known for being tough.