Scott Caan looks like a really great choice by looks. I have never seen him act though. Well, Scott can say "besides if I ever need advice who could play a better Sonny than my father." James Caan could coach Scott how to play Sonny.

I don't know his name correctly, but I think it's Giovanni Ribisi. Someone way back picked him to play a very young Sonny, and I think this is the best choice because he can act!

Leo isn't too masculine. Brando didn't/doesn't have a masculine voice, but his face and body and acting skills more than made up for it. Leo's face and body structure isn't tough enough to play Sonny. And when Leonardo Di Caprio tries to make a tough face, he looks like a soft boy trying to make a tough face...he just doesn't pull it off.

-A Streetcar Named Desire-

Stanley: You want a shot? (offers liquor)
Blanche: No, I rarely touch it.
Stanley: There's some people that rarely touch it, but it touches them often.