Upvote:4
Yes, you need a visa. The United States does not recognize the idea of visa-free transit, you will have to go through Immigration and then go out again.
http://canberra.usembassy.gov/transit-visa.html
The US has a C-1 Transit Visa that's supposed to be used for cases like yours, but this is apparently just as is difficult, time-consuming and expensive to get as a regular visa.
Is there any way you can change your flight not to go through the US? There are plenty of direct flights from Canada to Europe.