Hello, I’m a native English speaker. I’ve never heard this expression before but I can tell you that the only time there is a reason to use the word “suns” is if you’re talking about planets that have multiple suns. As you know, Earth has one sun. But there are a few planets that have two or more suns. Hope this helps. ☺️

This is from Gone with the Wind. It's just the author's style choice. It does sound much better than the more ordinary 'hot Georgia sun'. The plural 'suns' has a symmetry with the plural 'veils' and 'mittens' before it. And the plural means 'the' is unnecessary. This choice just sounds nicer even though it's not standard.

Hi Darla, I am from the southern US and have definitely heard references to the "hot Georgia sun". If the phrase was written, I am wondering if it was a typo (mistake). I have never heard sun in the plural. I hope this helps. :)