The award is presented based on the Canadian nationality of the director, not necessarily the song or recording artist; there have been a number of instances where directors have been nominated or won for videos that were created for songs by American or British artists.
The award is presented to directors who are Canadian citizens, regardless of whether the song or recording artist is American or British.  There have been cases where directors have received recognition for their work on videos that were produced for songs by musicians from other countries.