Hi, I am considering a purchase of a sealed MacBook Pro 16 inch from eBay seller, claims there is three-year AppleCare plus warranty tied to the serial number, if I purchase this device, will the AppleCare plus coverage follow to me Automatically?

You best check with Apple; you are buying a used device (never mind that it is supposed to be sealed - it is no longer considered new because the original buyer is selling it to someone else). Now, I recently purchased something similar and yes, there was some time left on the original Applecare plus. The seller gave me the serial number and I checked it on this site:

https://checkcoverage.apple.com/

In may case, the Applecare plan was listed and it showed a future expiration date. So, you can either try to have him email you the serial or have him go to that site and send you a screenshot of the result.

AppleCare can be formally transferred. Transfer your AppleCare plan - Apple Support --> https://support.apple.com/HT202712

Note that the "formal" transfer requires the seller to call Apple and give them all the details (including the buyer's name, address, etc). If you'd rather not do that with an ebay seller whom you do not know, then you can do it once you get the machine - that is if there is Applecare showing for that serial number.

Applecare is really tied to the serial number and transfers with the device, so you will be able to use it if you need repair service; however, it is easier in the Apple eco world if it is registered in your name/Apple ID.