Claims to U.S. Citizenship
The ACS office can provide information and assistance to someone who believes he/she (or his/her children) has a claim to U.S. citizenship, including registration of children born in the Montréal area to U.S. citizen parents and who have a claim to citizenship at birth. We recommend that any claim to citizenship is documented as soon as practical after birth or after someone is first made aware of a possible claim.
In order to register the birth abroad of child under the age of 18, the U.S. citizen parent must appear in person at the Consulate with the following information in order to complete a Report of Birth Abroad application, which requires payment of a US$40 fee:
Proof of U.S. citizenship for one or both parents - at the time of the applicant's birth
An original civil birth certificate of the child showing both parents' names
Identification for the child (preferably with a photograph)
An original civil marriage certificate for the parents, along with original evidence of the dissolution of any prior marriages for both parents
Affidavit of physical presence and parentage if the child was born to an unwed U.S. citizen father
http://canada.usembassy.gov/content/textonly.asp?section=travel&subsection1=usconsulates&subsection2=&document=mtlacs