no, they're still American. Canada is a country in the continent of North America.
"American" is the common term used to refer to citizens of the
United States of America.
Most other nations have names that can easily be converted to nationalities.
Britain -> British
Canada -> Canadian
India -> Indian
China -> Chinese
The USA doesn't work so well because
the Nation's name isn't one word and is more a description of itself, rather than a title.
So, either the people call themselves "United Stat-ians" or "Americans" or just refer to themselves as "Citizens of the United States (of America)".