Does anybody believe that there should be wizarding governments in Canada and Mexico that would be separated from the wizarding world of the United States of America, and its own government, MACUSA?
Canada and Mexico are countries part of North America, and not the United States.
And here's what I see the respective magical governments of Canada and Mexico would be:
Canada
Canadian Ministry of Magic (Fr. Canadien Ministère de la Magie)
Headquarters: Ottawa, Ontario
Leader: Canadian Minister for Magic (Fr. Canadien Ministre de la Magie)
Mexico
Mexican Federal Office of Magic (Sp. Oficina Federal Mexicana de Magia)
Headquarters: Mexico City, Mexico
Leader: Mexican Chief Administrator for Magic (Sp. Administrador Jefe Mexicano de Magia)