It's assumed that the huge majority of Canadian photographers have carried out some photography in Canada, so this category simply subsumes Canadian photographers as a subcategory; Canadian photographers are not additionally listed individually below.
As for non-Canadian photographers, they are listed if they have done a substantial amount of work in Canada (at a minimum, one book devoted to Canada) or if their work in Canada was of unusual historical or other significance. Non-Canadian photographers who have merely made short visits to Canada and had miscellaneous photographs published should not be specified below.