It's probably running Canadian firmware.

Rumor: Hulu May Require Cable Subscription For Free Streaming
http://www.tomsguide.com/us/Hulu-Authentication-time-warner-comcast-NBCUniversal,news-15031.html

 

Does anyone here know how to change the firmware to the US version on a Sony?

 

Well Sony sees that TV on a Canadian IP so it'll only send you the Canadian firmware. Unblockus uses DNS poisoning (faked DNS zones) to redirect a connection to Hulu through a US based proxy.

This will not work the same for a connection to Sony ... that will go directly and they will know you're in Canada.

You could try a VPN router setup with a USA IP and connect the TV to that. That should do the trick I would think... unless Sony uses the TV's serial number to determine that it's a Canadian TV... in this case you'd have to get into hacking the TV's ID.