The "third heaven" spoken of by Paul in the recounting of what undoubtedly was his vision in 2 Corinthians 12 verse 2 was a vision of Christ and the saints in glory in Jerusalem during the Kingdom age, the Millennium. Heaven and earth are terms often used metaphorically in the Bible to represent ruling power (heaven) and those ruled (earth).
- Take a look at Isaiah 65:17,18 For, behold, I create new heavens and a new earth: and the former shall not be remembered, nor come into mind. But be ye glad and rejoice for ever in that which I create: for, behold, I create Jerusalem a rejoicing, and her people a joy. (also compare Isaiah 2:1-4). The New Heavens spoken of here is clearly Jerusalem and the new earth her people.
- Now take a look at 2 Peter 3 and count the number of "heavens and earths" there are in that chapter. What is said of heaven and earth number 3? This clearly refers to the Kingdom of God and is the fulfilment of the Lord's prayer "Thy will be done in earth as it is in heaven." Also note Numbers 14:21 "As surely as I live, all the earth shall be filled with the glory of the LORD."
Here is a link to material on the website which will be useful to you in answering your question (please click on the title):
The Kingdom of God on Earth
I hope you have found this helpful.