Another way to say "What are the chances?" would be "what are the odds?" "What a coincidence!" also works, in almost all cases. It's basically an exclamation about how rarely the event would occur. Coincidence implies a pairing or doubling of events. i.e talking about a plane, as a plane flies over head.

No, but they are related. You can say ´what are the chances´ when anything unlikely occurs but ´what a coincidence´ can only be used when an unlikely event occurs as a result of unrelated events or circumstances. To say what are the chances another way, you could say: What are the odds? What a fluke! or just, Fluke! - but these 2 can only be used in some circumstances.