It looks like the Samsung Galaxy S3 LTE version is getting updates pushed to it. The new 4.1 update has been a long time coming for the GS3. The new update is just over 324MB so make sure you are connected to power and have WiFi enabled if possible!
Other Canadian carriers like Wind aren't showing any updates quite yet, and this isn't really a big surprise as Wind isn't really known for pushing out updates as fast as mainstream carriers. The Galaxy S3 came with Android 4.0 from the factory but that soon changed when it got root and Jelly Bean ROM's came out for "The Next Big Thing".
It is being reported that the Samsung servers are getting increasingly slower but with the amount of GS3's that are being updated it's to be expected. If you haven't gotten the update pushed to your device yet you can try and manually force it by the following steps:
Settings > About Device > Software Update > Update
Source Howard Forums Blog