hey,,
as far as i know, and i may be wrong, so if i am, plz correct me, they are very similar.
I am at monash uni doing a b business course majoring in accounting, and monash also offer commerce as a major in another campus.
The only difference i have found so far is that commerce offers finance as a major, whereas b of business does not offer finance but banking and finance.
If there are more differences, plz let me know too, as i am slightly confused in this area too.