We are setting up new DB servers in a new WAN location and need to transfer the DBs over (over 2TB). The existing DBs will still be live and being modified while the the data is being migrated so after the export (either SQL export or VM snapshot) we will import it (the DB or VM) at the new location. Given the sites are far away it could be a few days for the data copy to be moved to the new site.

What's the options to sync the changed data with minimum WAN usage? Is there an offline export of only changed data option?

What will be the role of the new DB servers? Continuity of bussiness/Disaster recovery/Pool machine/Read-only databases for statistical,BI or OLAP queries ? Which version do you use?

Depending on the database but ERP & BI mostly. Data input continually happens during the day and large jobs run at night from other sources. They range from 2000 to 2008 R2 but let's say all are 2008 R2 to keep it simple. I've been looking into SQL snapshot and merge replication.. Would this work in this situation or would you choose another solution?

If it is for continuous syncing - transactional replication with the initialize snapshot from a backup option. Then ship your backup via FedEx or something like that.

If you are interested in a one time differential - a differential backup after the initial backup is restored on the destination server is the best option.