Hi,

Is it possible to register .ca domain name as American National (or as an International Body) ?

Here's your answer:
http://cira.ca/faq-canadian-presence-requirements/

Dot-ca domain names are reserved for Canadians—people and organizations that meet CIRA’s Canadian Presence Requirements. You can find the information you need about the requirements in the following Frequently Asked Questions.

You can check http://baremetal.com/domains/ca_faq.html#registrant for details

Short answer: No
Longer answer: Maybe, under limited conditions

http://cira.ca/assets/Documents/Legal/Registrants/CPR.pdf