Actually, there is no IP address restrictions on accessing the PSN itself.
However, individual content CAN be blocked by IP if a publisher desires. For example, all movies, music and anime on the PSN is in fact region locked by IP address.
I can confirm that even with a Japanese PS3 and Japanese PSN account, I cannot access most of the video content from the Japanese PlayStation Store.
Also, it is important to note that games can be region locked based on the console region as well. For example, if you make a US PSN account, you can buy, download and install Persona 4 Arena from any country on any region PS3. HOWEVER, the game will refuse to boot unless your PS3 is a USA/Canada or Mexico/South American model.
However, luckily Black Rock Shooter does not contain either restriction.
Note that USA and Canada both have the same PS3/PSP/PS Vita models, so it is 100% impossible to region lock something to work in the US but not Canada based on the hardware itself. The most they can do is IP lock you from purchasing it, for online purchases at least. They can't block physical media at all though.
It is important to remember that PS3, PSP and PS Vita are NOT region free consoles, they are simply consoles that give the developer the CHOICE to leave the game region free or to region lock it, and the vast majority choose not to region lock.
If you are curious as to how many PS3 region codes there are, there is a list here:http://www.ps3devwiki.com/wiki/Regions
The PSP and PS Vita use the same region codes.
It's also important to note that the devs can specify precisely what regions are allowed and which are not. For example, the Japanese version of P4A allows Japan, Hong Kong, Taiwan, Korea, and Singapore / Malaysia, but blocks all the other regions.
The Japanese demo version of Metal Gear Rising on the other hand blocked all regions except Japan.