I have 2 wordpress site that is using Multisite

I have 2 wordpress site that is using Multisite and mutliDB.
Currently i am trying to sync the production content to the staging one.

-i have tried copy over the public_html over and the DB, including changing the url
-import DB using cpanel

but then it show "Error establishing a database connection" when trying to load the site
is there other way i can migrate the content over as the file size are over 100GB.