Here is a list from the US IRS database of organizations with US 501(C)(3) charitable type status that are located in Canada.  You can search Publication 78, Cumulative List of Organizations described in Section 170(c) of the Internal Revenue Code of 1986.

Some of these organizations are US “Friends of” organizations.  Others are established Canadian charities that have applied for US 501(C)(3) (generally a bad idea).  If you know that an organization has received 501(C)(3) you can try to find their Form 990 at Guidestar – this provides additional information on the organization compared to the information contained in the Canadian T3010 Registered Charity Information Return located at http://www.cra-arc.gc.ca/chrts-gvng/lstngs/menu-eng.html