Have you noticed the difference between the Canadian and US model? The front fore grip is attached via piccatinny while the Cannuk is permanent. I wonder why that is?
The differences in the U.S. version are all about silly laws as well. Canadians are by no means the only people who have governments dicking around with their firearms.
The "standard" U.S. version of the TP9 is a "pistol". It has no shoulder stock and no foregrip. The presence of either would render it a "Short barreled rifle" under the National Firearms Act, possession of which is a federal felony without authorization by (and paying a tax to) the BATFE. You also need permission (in advance, by sending in a form) to transport an SBR across state lines, and some states do not allow you to possess these types of firearms at all.
It is roughly analogous to "non-restricted" vs. "restricted". The only way to avoid the SBR thing is to have a barrel 16" or longer, or an overall length of 26" or longer - or get it classified as a "pistol". It is the same reason why the vast majority of "M4"-type AR's in the States have 16" barrels, and why AR pistols have no stock and no foregrip - and companies like RRA and CMMG have tons of warnings in their literature about putting stocks on pistols.
On the TP9, when I first shouldered one, my first thoughts were.. "Wow, this is small". If you don't have the opportunity to shoulder one before buying... think "pistol with folding stock" not "MP5-type thing". The TP9 is very cool, but it is very small, and very light.
For this type of firearm, I decided to go with a RRA 7" 9mm pistol, which we are able to put stocks and foregrips on to our heart's content. It is definitely a bigger, heavier firearm - but for my money it feels more "substantial" - plus you can get 10 round mags and a much wider selection of accessories. Having said that, I'd still love to add a TP9 to my collection.
Here are some pictures of my 9mm. These are unfortunately pretty hard to find right now. These are all the same gun. Current incarnation is on the bottom and in the video.
Video:
http://www.youtube.com/watch?v=8Bj4-lluJOs