Chance and opportunity mean the same thing.
Although, it's worth noting that Chance is a statistical term.
for example:
There's a 50% chance of rain today
There's a 25% chance you'll get a blue m&m out of the bag next.
Chances are I will score better than my friends will on that test.
You can't use the word opportunity when you're talking about probability, instead you have to use the word chance.
Chances are there's going to be a war in Lebanon this summer....
you can't say there's an opportunity for war.... because there's always the opportunity for anything and everything to happen, no matter how small the CHANCE of it happening are...
There's an opportunity for it to snow in Saudi Arabia, but the chances are very very small.
in summary,
chance is like the roll of dice or the flip of a coin, but opportunity is a window of time/conditions where you can make something happen.