LB for Anyconnect VPNs for Active/Active DCs

Suppose I have two DCs, DC1 & DC2. I have FTD clusters in both DCs acting as VPN concentrators to terminate the remote access VPN anyconnect connections.

I understand that within the DC, clustering will take care of the loadbalancing/sharing. But how do I distribute remote access anyconnect VPN traffic equally between the two DCs? Do I need to use external GLSB? Any recommendations for GSLB e.g. on Azure or AWS?

external GSLB is the right solution here. AWS or Azure should both work fine. You can also look at private options such as F5 GSLB.