have no criminal or immigration-related convictions,
convince an immigration officer that you have ties—such as a job, home, financial assets or family—that will take you back to your home country,
convince an immigration officer that you will leave Canada at the end of your visit, and
have enough money for your stay. (The amount of money you will need can vary. It depends on things such as how long you will stay, and whether you will stay in a hotel, or with friends or relatives.)
To summarize the above, you will need to have proper I.D. (like a passport) to travel to Canada, as well as meet several other requirements to travel to Canada, including things like be in good health and that you will leave Canada at the end of your visit.
Here are the Travel Documents you need to enter Canada:
Essentially, you will need a passport to travel to Canada no matter where you are from the world.
Documents you need to enter Canada from a foreign country (Including the United States)
According to Wikipedia,
Canadian law requires that all persons entering Canada must carry both proof of citizenship and identity. A valid U.S. passport or passport card is preferred. A birth certificate, naturalization certificate, citizenship certificate, or another document proving US nationality together with a government issued photo ID (such as a driver’s license) is acceptable to establish identity and nationality. However, the documents required to return to the United States are more restrictive (for example, a birth certificate and photo ID are insufficient) – see the section below on Return entry into the U.S..
To summarize the above, you will need valid government I.D. that confirms which country you have citizenship in, as well as your identity.
A passport is the best identification to validate both of the requirements above. I highly recommend you get a passport if you want to enter Canada. After all, a passport is an official travel document that allows you entry into many parts of the world.
If you want to travel anywhere outside the Unites States, you basically will need a passport. Very few countries will allow you to travel to them without a passport.
Here is the full link to Wikipedia’s article on Entry into Canada for Americans.