If you look at the date of the original post, you see it was almost 3 years ago so I am sure the original poster already made his trip but if you want to verify that US green card holders don't need a visa to visit Canada, you can see it on the website of Canada immigration here:
http://www.cic.gc.ca/english/visit/visas.asp#exemptions
Visitor Visa Exemptions
Many people do not require a visa to visit Canada. These include:
* citizens of .....
* persons lawfully admitted to the United States for permanent residence who are in possession of their alien registration card (Green card) or can provide other evidence of permanent residence;
* ....
This does however not work in reverse, that is Canadian PR's who want to visit the US may still need a visa, depending on their citizenship.