Both the United States and Canada allow their residents to hold dual citizenship--that is, to be a citizen of two countries at the same time. You can become a dual citizen in two ways: with or without naturalization. Without naturalization means that you don't have to apply; because you or one of your parents were born in the country that you don't currently reside in, you automatically hold citizenship to that other country and the country you reside in. With naturalization means that you do have to apply by filling out certain forms, complying to certain standards and taking specific immigration tests. Once you are given citizenship via naturalization you do not have to give up your other citizenship, and you will thus have dual citizenship.
Becoming a Dual Citizen Without Naturalization in the U.S. and Canada
Determine your parents' birth place. If you were born in Canada but one or both of your parents were born in the United States you automatically have dual citizenship. The same is true if you were born in the United States but one or both of your parents were born in Canada.
Contact the Consular affairs offices in Canada and the United States to ensure you can become a dual citizen. You'll be asked to provide details about yourself and your family, including your birthday and birth place, and the citizenship of your parents.
Obtain a certificate of citizenship from the Unites States and Canada to prove that you are a citizen of both countries. You can obtain these certificates once you've determined that you are a dual citizen and once you fill out the proper applications. The Canadian application form is simply called "Application for a Citizenship Certificate (See Resource 1 for the form). American application form is called an N-600 (See Resource 2 for the form).
Dual Citizenship With Naturalization for Canadian Citizens
Apply for and hold a green card (permanent resident card) for the United States.
Stay in the United States for 5 years once you obtain your green card. You must be physically present in the United States for at least 2.5 years of this time, understand the English language and U.S. history and government, be at least 18 years old, and have a good moral character and allegiance to the U.S
Stay in the state or INS District where you are applying for 3 months prior to applying for citizenship.
File your official petition for citizenship with U.S. Immigration Services. You'll then have to appear for an interview with an immigration official who will consider your application and your interview answers to determine if you can take the final oath of allegiance to the U.S.
Dual Citizenship With Naturalization for U.S. Citizens
Obtain permanent resident status in Canada by filling out the appropriate application. You must be at least 18 years old.
Prove your eligibility to Canadian officials. You must have lived in Canada for at least three years in the past four years. You can count the time you lived in Canada prior to obtaining your permanent resident status if that time falls with the four year period. You must prove your knowledge of English and/or French to a Canadian Immigration official by completing a written test to prove this. You miust also demonstrate that you have not been convicted of a criminal offence within the three years that you have applied for citizenship.
Complete the knowledge of Canada test. You must understand the rights and responsibilities of Canadian citizens and Canada's history, values, institutions and symbols.