Since you are rooted, GooManager would work for you. A number of people with Canadian versions of the SGS3 have reported that they used GooManager to flash the d2att version of CWM with complete success.
To install with Odin or Heimdall you will need a version of the recovery packaged as a .tar.md5 or .tar. Be sure to get the most recent version of CWM. It can be found with a search of the forums. There are tutorials available about using Odin, in short put the .tar.md5 into the PDA slot. Bear in mind that I don't use Odin, read about it for before using. Caveat, some older ROMs may require an older version of the recovery.
(I edited my previous post to correct a misstatement on my part, I changed bootloader to recovery)