For those of us Celcius dyslexic,
-30C = -22 degrees Fahrenheit
I'm not aware of any information about tempertures in that range "killing" the battery. On the Classic/1st Gen Prius you'd see a little turtle on the display and performance could be severely hampered when that cold.
On the current generation Prius you'll experience some reduction in performance as the battery is very inefficient when that cold. Fuel economy will suffer as well when that cold.
I'm not too familiar with the weather in your region, but unless you experience particularly long periods where it stays that cold I'd expect a Prius to do just fine. Many people in the US states of Minnesota and Alaska drive a Prius and they experience temps colder than -30C not infrequently as well.
A bigger concern, however, is that you would likely be completely unable to have a Prius serviced should you have any problem. This isn't a car you can cobble back together with panty-hose and duct tape..it requires specialized computers and techs with specialized training to repair them...though routine service doesn't require any special training at all.