Multi-site Failover Cluster Instance for HA and DR to alwaysON Availability Groups In my company we have chosen to implement Multi-site SQL Server Failover cluster.
Basically Data center A  has 2 nodes (Active/Passive) and Data Center B geographically located acts as the DR. I believe there will be a SAN replication from  Data Center A Data Center B.

If in future we want to implement a Multi node  AlwaysOn and availability group HADR solution. By that i mean (Data center A  has 2 active node and 2xSANs, and DBs are part of a group. Data center B has an  Active node and its own SAN which act as a DR site). 
Can you guide me on how to implement this process or articles that explain this in details.

How can I migrate from a geo-clustreing to an High Availability Disaster Recovery? and what should I consider?
The best practice for your scenario is: 2 nodes in Location A with their subnet say Network_A 192.168.1.x and one node in location B (DR) with subnet Network_B 192.168.2.x.

The weight in Location A is more so you don't need to add disk or folder to your cluster. Your failover Cluster will take 2 IPs one from Network_A and the other from Network_B and your Listener too. The Network_B IPs appears in your cluster offline unless you Failover the DR site, in normal cases you can use SQL database in your DR as read-only.

One important thing: if you have SAN replication don't make your Databases as part of this plan nor part of RDM (raw mapped drive).