Samsung Canada is holding an interactive learning session with Canadian carriers for training towards the Galaxy S III Canadian release. LINK HERE
There is a good possibility that it will release either right after training, or earlier than that. Rogers is most likely going to be getting the LTE variant (Just look what happened with the HTC One X) however the T-Mobile version passed FCC with an HSPA+ model which could very well be the Quad-Core variant, and normally TELUS gets the same phones. As for bell, depending on what part of Canada you live in, they usually run on the same towers as TELUS - For example, I'm in Kelowna BC and they operate through TELUS' towers.
Because I live outside of the 1700 MHz frequency I wouldn't have need for an LTE Device, and because my current phone is starting to fall apart I've decided to just order the international version online (Ships on May 29th if you order through Negri Electronics).
Hope this helps.
Service Provider: TELUS (Canada)
Phone/Model: Samsung Galaxy S IV (SGH-i337M)
Build Version: JDQ39.I337MVLUAMDJ