Q: Is WPA enterprise available for apple tv3

The Apple TV does not support enterprise networks.

If you have a Cisco wireless network, they have an option of creating a secondary SSID without Enterprise (i.e. make a WPA-PSK SSID), then link that SSID's multicast traffic to the primary SSID that your other devices use.

http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_tech_note09186a0 080bb1d7c.shtml#vlanselect

For a non-Cisco environment, if your wireless networks all end up on the same back-end VLAN, you could setup an access point on that same VLAN that is using WPA-PSK and only use that access point for AppleTV units.  Not as clean as Cisco's option (where Cisco's option doesn't require additional access points, just different settings), but it would be a work-around.

One other option, Cisco's article mentions Avahi http://avahi.org/ , which can replicate multicast from one VLAN to another VLAN.  You could setup your AppleTVs on wired networking, and use a computer running Avahi to replicate the Bonjour traffic between the wired network and the wireless network that your other iOS devices are connected to.

Overall it is all ugly because AppleTV does not have WPA-Enterprise, but there is only so much you can do until someone decides to add that to AppleTV.