can you be a citizen of 2 countries?

Depends on the countries but Canada and the U.S. do allow Dual citizenship I believe. You will still need to produce a passport at the border.

Yes, you can be a citizen of two countries, including the US and Canada. You still need a passport. How else would they know that you are a citizen?

Do you know how to use google? of course its called DUAL Citizenship..

Any country with diplomatic relations of the US you can have citizenship in..

P.S Why would you not be able to ?

It happens everyday? and you truly don't need one just to go there.

Unless you were granted the second citizenship at birth - for example when Ted Cruz was born in Canada or Obama's father was a British citizen - you can't. If you are granted citizenship in a foreign country you automatically renounce your US citizenship.

you always need a passport when traveling from one country to another

From what I have heard, your parents need to be citizens of US, and then YOU need to be born IN Canada.