Can a person travel to Canada with a green card?

Yes but a gold card would be better.
Visa would be better yet
or Master Card.

A green card is a U.S A government issued document, it has nothing to do with coming into Canada...they are two different countries under different governments, with different laws. You will have to show your passport or citizenship papers to the border guards when entering into any other country, including Canada. So the answer to your question is no a green card will not help a citizen of a different country cross into Canada

Not anymore. Now a greencard holder needs a visa to enter Canada (unless he holds a passport of country that falls under visa waiver program with Canada).

What is your citizenship? If you have a green card, you are only permitted residence -- you are not a citizen. You will have to follow Canada's rules for citizens of your country. If a visa is required, you have to get a visa.

green card and passport - but no visa.

Many people do not require a visa to visit Canada. These include

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;

Depends what country they are a citizen of.

With green card and your valid passport of your country, you can enter Canada without visa and you can come back to US.