In a statement to the fine folks at MobileSyrup, Samsung has verified that all Canadian models of the Galaxy S III will include free (for two years) an extra 48GB Dropbox storage.
New GS III users will receive a basic 2GB of free space with Dropbox (It is permanent). When they create their own Dropbox account or link their existing account to Samsung Apps, the user will receive 48GB more space through a promotional offer, for a total of 50GB. This is available for 2yrs.
This leaves us with two questions -- what happens to your files at the end of two years if you decide not to continue the 50GB plan, and why Verizon and AT&T decided against it. We can guess at the answer to the first -- you'll likely be given a grace period to get anything from the cloud you want to keep before you lose 48GB worth of your storage. Dropbox wants your love, and your money, and they know they won't get either if they delete your files willy-nilly.
The answer to the second part, well, that just escapes us.