this is from the us dept of state website:
ENTRY/EXIT REQUIREMENTS: Entry into Canada is solely determined by Canadian Border Services Agency (CBSA) officials in accordance with Canadian law
. Canadian law requires that all persons entering Canada carry both proof of citizenship and
proof of identity. A valid U.S. passport, passport card or NEXUS card
(see below) satisfies these requirements for U.S. citizens. If U.S.
citizen travelers to Canada do not have a passport, passport card or
approved alternate document such as a NEXUS card, they must show a
government-issued photo ID (e.g. Driver’s License) and proof of U.S.
citizenship such as a U.S. birth certificate, naturalization
certificate, or expired U.S. passport. Children under sixteen need only
present proof of U.S. citizenship