If I want to enable failover
clustering for both Exchange 2010,
ensure zero downtime. What are the
First, failover cluster DOES NOT GIVE ZERO DOWNTIME. Bad news, isn't it - happens because you did not read the documentation. Failover cluster will start exchange / a VM on another server if the first fails. It takes some time (seconds) to realize the original system is down, plus the time it takes for the system to start (larger for a VM), so while the time is small, IT IS NOT ZERO DOWNTIME.
Second, Exchange can do that a lot better WITHOUT a failover cluster. Exchange has it's own cluster mechanisms that can work with multiple data copies... which means one less thing that can g o wrong (corrupt files in a node crash), so it is (a) superior to failover cluster and (b) faster in switching.
So, I sgugest getting your requirements straight, and then using Exchange integrated mechanisms to ensure uptime.