MI date! But it's in July which is already jam packed with concerts for me...so not sure if I can swing another one.
As far as the openers, Avenged Sevenfold aren't my cup of tea but they're pretty highly regarded in modern rock/metal. Volbeat are highly thought of, too. Gojira have a lot of screaming in their music, but they're considered one of the best modern metal bands. Again, none of these are my cups of tea, but they seem like good fits for Metallica.