Use NetApp DataMotion, if moving to another aggregate inside the same NetApp Controller (A > A or B > B)
https://library.netapp.com/ecmdocs/ECMP1196995/html/GUID-A03C1B1E-3DE2-455D-B5AD-89C1389EF0C8.html
If it is to another controller (A > B or B > A), You are going to need downtime to do this either way, so I would either provision a new boot LUN, and rebuild ESXi, or snap mirror the volume over to the other controller and reboot the host for the cutover.
Personally, I'd provision the new boot volume, and rebuild. That gives you some fall back protection, and tight change control.
Jon