DNS/GTM Activesync Load balancing

I have two data centers where APM front ends activesync traffic to backend LTMs that direct traffic to the actual exchange server. The only issue is that over time in an active/active data center environment, the activesync client will end up establishing APM connections to both data centers due to it re-resolving the activesync FQDN.

What is the best way to distribute the wide-ip responses to both data centers while maintaining client affinity/persistence to whichever one it happens to receive when GTM first responds?

Thanks.