FWIW, I wouldn't use CORBA unless you have existing CORBA-based infrastructure you need to interface with.
CORBA was OK in its day, but it is a "dying" technology, and you are going to have a hard time getting the necessary support going forward. There is also a pretty steep learning curve.
I'd stay away from the Cocoa/Gnustep stuff too, if you want something cross-platform, as it really isn't very well supported anywhere other than OS X and iOS.
Rather than mastering these legacy technologies, I think your time would be better spent figuring out how to use Web Services, SOAP, or other mainstream cross-platform integration technologies.