Unity can provide replication over the WAN. Just need to have enough bandwidth allocated to the SQL replication. Failover will also ping the remote server to make sure it's alive. If the WAN link goes down, failover could kick in... so you have to play with the threshholds to make sure its "really down" The first replication will take awhile, but after that, it's fairly small changes. You could even set the replication pattern yourself in SQL if you want to only replicate once a day, or twice day. But right now, out of the box, its' fairly "live".
Failover is failover. Everything is available ready to go. It does to take about a minute for it failover completely with TSP... little longer with PIMGs.
hope this helps