You would need to have some sort of software capable of combining the footage from two Hero 7 blacks, it would also have to be able to calculate and adjust the overlap angle to give a 3d view. You would then also have to make a sturdy undwater rig to hold the camera's in place that doesn't allow for any flex of adjustment between the two angles. I think this could work out to be very expensive. It's certainly not something that GoPro currently supports. You may be better off just trying to find a stereoscopic camera system that has all of this worked out already.
GoPro only made the Dual Housing for Hero Black3 plus...and have not thought it worth it to make one again...I am at least looking for a 3rd Party to have made one for the Black 7.
@snowybluff1421, you can sync/control multiple GoPro cameras using Smart Remote (connected through the camera's Wi-Fi). Note that Wi-Fi doesn't work underwater though. There might also be some third party systems that can sync GoPro cameras for multi-camera shoots, however, we do not have any further information about these devices.
