No one knows yet, and since this version of JB is not out globablly for the S3, you'd have to wait for Samsung to release the software to the carriers.
Question, what does 4.2.2 bring to the table that you absolutely must have?
One thing to keep in mind with Apple, although they may bring a new iOS to their older devices, it's usually a watered down version, so in my opinion, I'd rather wait a bit and get the full functionality on a Samsung, than get a crippled version on Apple products.
4.2.2 for tablet or phone allows for multi window fuctions among other things. Bug fixes as well. Now 4.2.2 came out in February and there are a lot of places you can learn to update outside your provider. Rogers doesn't really do anything to the factory operating systems so I have no idea why it takes them so long to get it, but even still I am too scared to update on my own so I keep waiting. Rogers is a very slow company for updated stuff though so I am not sure why this surprises me so much.
So mult window is what you are looking for mostly? I have it on my Note 2, and never use it, but that's just my opinion.
It's actually nothing to do with Rogers at this time, Samsung hasn't released this software for the S3 globally, so you should try contacting Samsung to see what they say.
If the absolute latest software is the most important feature to you, rather than the actual features a phone has, you should probably pick up a Nexus device, that sounds like it may be more suitable for your needs.