Hi,
You definitely want to avoid redirects where possible, so scratch option number 2. Redirection causes you to lose about 10% of the authority that page has built up. Google tends to prefer pages that they have known about for a while.
If you were to do option 2, you'd also have to update all of your internal links to point to the new page, as well as outreach to any external linking sites to have them update.
All you need to do is take the source code for the variation page and make it the source code for the original.
It sounds like you may have used Google Content Experiments. If that's the case, the additional URL created for your variation doesn't need to be excluded from crawls or disallowed, Google knows it's there and there's no other way to get to it other than the code snippet they utilize to send your sample to the variation.