1. What is the network bandwidth like between the two data centers.
2. How much latency can you afford to have. Bearing in mind checking the inventory on the other sites. (Near real time, nightly synching)
3. Will the users on different sites be changing the data in the same tables that are replicated.
From the information that you have provided I think you will probably be looking at Peer to Peer or Merge replication.
I have setup the two way replication before between and london and Singapore servers.