To visit Canada, you must:
have a valid travel document, such as a passport,
be in good health,
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 like how long you will stay, and whether you will stay in a hotel or with friends or relatives.)
Americans do not need a visa to enter Canada
Transport companies, such as airlines, must make sure you have proper, valid travel documents when you enter Canada. If you do not have the proper documents, you may be delayed or unable to board the plane.
When you arrive in Canada, a border services officer will greet you. The officer works for the Canada Border Services Agency (CBSA). The CBSA protects Canada's borders and points of entry.
The officer will ask to see your passport or travel documents. Make sure that you have them with you and that they are not packed in your luggage. This will speed up your entry into Canada.
You cannot bring firearms into Canada.
More information here http://www.cic.gc.ca/english/visit/apply-who.asp