yes you can,,being a green card holder makes you a visa exempt citizen(crazy how a small piece of document can determine who you are)..
you dont need a visa so,yes you can travel to Canada no problem,,now,,once you land the immigration officers will most likely ask you questions to know the reason of your visit so,if you have that covered no need to worry...
source:me,Cuban citizen(cubans need a visa to travel even to planet mars), I have a green card.