I pretty much agree with what Jared(제리드 씨) described it for you. Just one thing. In my understanding 건너편 and 맞은편 are almost same that you can use both no problem. 건너편 is 'across the street'. And the long version of 맞은편 is, I think, '마주보고 있는 방향'(facing each other). When one place is across a street from the other place, they gotta face each other. That's why it's hard to say there's a difference. Good luck.

I've never noticed any practical difference between them, but a native speaker may be able to help you more. 반대편 -- the opposite side -- is related to 반대, meaning "opposite." 건너편 -- across from -- is related to 건너다, meaning "to cross." 맞은편 -- either across from or opposite from -- has a more complicated etymology. I believe it's related to a form of 맞다 that means "balanced." Quite literally, you're saying "on the side balanced to this one." As you well know, we often have more words than we need for any given concept. I believe this is just one more example of that. It's a beautiful thing.