I'm in need a high fantasy RPG campaign that is epic in scope, similar to The Wheel of Time. I even love the chosen one and/or chosen party of characters tropes and all. I'm looking for a system-specific OR systemless epic high fantasy campaign I can run.

Does anyone have any suggestions?

The Great Pendragon Campaign
Spans 80 years of Uther's and Arthur's reign
https://www.drivethrurpg.com/product/12405/The-Great-Pendragon-Campaign

The Mirkwood Campaign for Adventures in Middle Earth
Takes place between the Battle of Five Armies and the Lord of the Rings. Because Sauron's assault on Erebor, Dale, and Lake-town was only lightly touch in LoTR this was pretty good making the PCs feel like they were making a difference in Middle Earth.  Sadly now only sold for collector prices.

Thanks.  I'm familiar with and own both.

I am hoping I will be able to adapt whatever I settle on into my own customer setting.

Not sure how crunchy you want to get and I've never played this game myself, but I've heard good things: https://www.drivethrurpg.com/product/104176/High-Adventure-Role-Playing-Fantasy

Ok, with the caveats that not only have I not read the Wheel of Time, I've also not played any of these campaigns (and might be slightly drunk).

City of Brass for Swords and Wizardry came highly recommended to me when I asked a similar question a few months back. Albeit that it is running a little pricey at the moment.
https://www.drivethrurpg.com/product/266876/City-of-Brass-Swords-and-Wizardry?term=the+city+of+brass

You might also look at any of the campaigns published by Art of the Genre. They've done several campaign-length module series dual-statted for 5e and AD&D
https://www.drivethrurpg.com/product/265595/The-Complete-White-Ship-Campaign?
https://www.drivethrurpg.com/product/216406/The-Complete-Cities-of-Sorcery-Campaigns?
https://www.drivethrurpg.com/product/352958/The-Complete-Curse-of-Roslof-Keep?

If you're willing to do some conversion work, you might find something in the Pathfinder 1st edition adventure paths. This dude ran them all down on Youtube
https://www.youtube.com/watch?v=gVBViA2tNaU

If you don't mind a little do-it-yourself sandboxing, check out Red Tide by Kevin Crawford of Sine Nomine Publishing.

A nightmarish red mist has covered most of a world and the only place that the mist cannot approach is a continent and it's outlying islands.  Most of thecontinent is inhabited by "goblinoids" called the Shou who are highly xenophobic, and a good portion of the continent is inhabited by enclaves or refugees from the various other kingdoms of the world. They have built their areas up to be like the countries they originally came from.  There is a heavy East Asian theme in several of the countries, as well as something like the Swiss Cantons. 

Made originally for Labyrinth Lord there are spellcasting classes:half elves, shou witch, stiched sorcerer, and a monk like martial artist with several flavor oltions (ninja, shaolin, etc).

Two hex maps one with the countries labeled and one with just the terrain, arethere for convenience.  I am hoing by memory here but I think there is a mostly blank map that shows only the coastline in case you want the players to be explorers.

Alsonincluded in the book are new monsters, various demons and creatures associated with the Red Mist, called "Tidespawn".  There are some other cool things about the setting that I don't want to spoil. 

In addition to the awesome fluff, there are aids to generating adventures, mostly site-based but also stuff for generating adventure hooks and background.  If you are an amateur mapper then there are some tips for easy map making, that do not involve artistic talent.

Definitely worth checking out.

Kevin Crawford's Worlds Without Number and his Latter Earth setting are what I'm planning on running it in.