It is absolutely possible and legal to hold a Canadian and a US passport as is the case with my brother who was born in Canada to American parents, so he has dual citizenship with BOTH countries.

I carry two passports since I became a US citizen (2nd class US citizen, that cannot be President) 30 years ago. Yet the French Republic will not allow me to renounce my citizenship of birth. I have to sue to be able to do so... 30 more years of legal wranglings and millions of dollars? I'll keep the two passports and the legal fees.

Multiple citizenships are completely legal according to the US, and in my case, quite convenient. I have Spanish citizenship due to my grandparents being Spanish citizens, and US citizenship due to my place of birth.

When I traveled to Brazil, my US citizen travel partners had to get tourist visas which involved a consula visit and $130 in fees. All I had to do was flash my Spanish passport at the airport, and I was in visa-free and fee-free.

I am able to have 3 passports, as well. I am a citizen if Ireland, USA & Spain. I have the birthright to citizenship in Ireland and Spain. I am 2nd generation Irish and Spanish. I was born in the USA. Many people do not realize if you are 1st or2nd generation, meaning your parents or grandparents were from another country and came to the USA, that makes you 1st or 2nd generation and a right to citizenship to the countries your parents or grandparents are from. The birthright to citizenship stops at the 2nd generation. I am not sure about the criteria for all the other countries in the world but I am about my generational roots in Ireland and Spain. In fact, if I wanted, I could be a citizen of the UK, as well. It would be more difficult but when my grandmother was born in Ireland (south), it was still under British rule and oppression. Interesting, right? Check out your ancestry, you never know what you are able to posses.