DFS Question what would be a best practice

Hi guys, I have a question. I'm looking for what a best practice would be (best performance / best practice / best support)

I have 2 sites which are connected via VPN.

I would like to set up a DFS between both sites but the two sites have 2 different domains. 

My question is what would be the best way to set up a DFS. 

Should I 

A) Just join machine on site B to site A domain and create the DFS

B) Do a cross domain DFS which would require a two way domain trust I assume

C) Any other option I might not be thinking of

**Site A would be the master site and site B would be the replication in the event site A dies site B DFS would take over**

Thanks! :)