Distinction between primary and secondary sources varies somewhat between disciplines. This is especially evident when contrasting history with English literary studies.
In literary studies, the item (novel, play, story, image) itself is a primary source. Other documents created at the time of publication are generally considered to be secondary sources: contemporary book reviews and author profiles and interviews found in newspapers and magazines.
Contemporary publisher's catalogues and advertisements in other publications may provide insight into the history and reception of a book. This kind of material was often regarded as ephemeral and rarely saved, Some authors were meticulous at scrapbooking and keeping records that may be found in archival resources including online exhibitions and digital collections. Likewise, some publishers kept good records of sales but these may not be open to the public or otherwise hard to access, even if they are in public research institutions. An unpublished account of sales would be considered a primary source. To find author or publisher archives, try Googling the name with the word archive.
Search the library catalogue using the author's name in a subject search.
Look for entries with the name of the author by itself, or with subdivisions such as --Correspondence; -- Diaries; --Notebooks, sketchbooks, etc.
In reality, since the creators of the comics in the Canadian Whites are largely forgotten, there will not be much in the way of research material about them. They may appear in newspaper articles. Uses of pseudonyms complicates matters further. Some documentation may focus on other aspects of the person's career, for example work as a fine art painter rather than as a cartoonist.
Alternately, try a keyword search using the author's name and a word such as: diaries, journals, correspondence, letters
example personal name as subject search: seth 1962-
Interviews may be indexed in the "search everything" tool since it is designed to search digital content in addition to the library's book and media catalogue.
Googling the author, illustrator or publisher and the word archive will help you locate physical collections containing archival material pertaining to the person or corporate entity. If you're lucky, you may find that some of the items have been digitized.
example found Googling: lou skuce archive, returns some articles and a reference to items in the Toronto Archives