read the last paragraph in the link.....
Yes, so you are supposed to get your MMSI # from the fcc if you do international travel. For that, you need to get a ship's station license from them. Actually, you are supposed to get the station license for international travel regardless of the mmsi #. To make Canada happy, you need a restricted radio operator's permit. They will accept the US one from the fcc (nominal fee and no expiration). Good luck with the fcc web site. You can get there from here, but it's not easy.
Not sure what all the red tape's about, 'cause from my limited experience in Canada, no one checks or seems to care. With the mmsi # though, I wonder if it might be a case of who has access to the various data bases. Maybe your US only # is not made available to international rescue people. So if you have to press that button while in Canada, a US only # might do you no good, while the fcc one might be recognized. Just a guess.
Here's the link to the page where you register:
http://wireless.fcc.gov/uls/index.htm?job=home
Once registered, you can apply for a station license (I believe they call it a ship license) at a pull down menu at the upper left of the page when you log into the system. There are various help pages as well, though they are less than clear.