There is an add-on available for users to input product/variation Brand, UPC and EAN. In order to add upc ean values to variable products in woocommerce, please find instructions and free plugin here: Additional Product Fields.
Various merchants require you to provide Brand, UPC or EAN value when you are listing your products in their sites. If the merchant doesn’t already have the product that you are listing, you will have a compulson to provide these values. So, in order to list your prodcuts and avoid feed listing errors, you will need to incorporate these values in the product feeds.