The more relevant question is requirement to return to the US, because US border control (which controls entry into the US) has more strict requirements than Canadian border control (which controls entry into Canada).
Most US citizens can no longer return back into the US, from Canada, using only a driver's licence and birth certificateFor US Citizens - entering the US - by land (i.e. driving) or sea--above the age of 16 need a passport (or passport card, Nexus, or Enhanced Drivers license).
A BIRTH CERTIFICATE IS INSUFFICIENT--15 and younger can enter with a birth certificate (original, photocopy, or certified copy), or US consular report of birth abroad. I.e. no photo ID.
--18 or younger travelling with an organized and supervised school, religious, or other youth group, can also enter with a birth certificate
--Infants under the age of 1, not having a birth certificate yet can travel with birth record issued by the hospital, a letter on hospital letterhead or a letter from the doctor who delivered the child providing details of the birth, including the name of the child, time and place of birth, and parents names.
For US Citizens entering US - Travelling by Air (flying)--a passport is needed (or Nexus card) regardless of age. (with the possible exception of a young newborn infant).
https://www.tripadvisor.com/Travel-g191-s602/United-States:Crossing.The.Border.html (This page seems to be updated frequently)
FYI - The more lenient requirements for US citizen's to enter Canada are:--proof of citizenship such as a passport, birth certificate, a certificate of citizenship or naturalization, nexus
That said, A passport
may be required by your airline or alternative transportation authority, as it is the only universally-accepted identification document, and is therefore recommended.
http://www.cbsa-asfc.gc.ca/travel-voyage/td-dv-eng.html#_s2aFor Passport fees see:
https://travel.state.gov/content/passports/en/passports/information/fees.html(Note that children's US passports expire every 5 year, rather than the 10 years for adults).These laws are is subject to change.
Hope this is helpful.
(At the very least they'll save me some time, next time I need this info)