From what I've seen (not much), most men have one testical that is a little larger. It doesn't seem to be of much concern, though nobody here will be able to tell you if it is cancer based on what you've posted. You will actually have to see somebody who is licensed in heath practitioning to make an official call.

I've included a link from the Testicular Cancer Resource Center about how to do a self examination. At one point on the page, the site states, "Don't be alarmed if one testicle seems slightly larger than the other, that's normal."

http://tcrc.acor.org/tcexam.html