Two titles that have not survived are The Stepsure Letters and Tiger Dunlop's Upper Canada. Janet Friskney's New Canadian Library (University of Toronto, 2007) helps explain why. She has a table of the unit sales for each book from 1958 to 1979. There are 73 books with 10 or more years of sales data. Eight of the books averaged sales of less than 500 copies a year, including The Stepsure Letters and Tiger Dunlop's Upper Canada. The other six are also no longer in print.
I'm not surprised at the low sales as both books look unappealing (the back cover blurbs are no help) but The Stepsure Letters does have an introduction by Northrop Frye that makes the book worth finding.
NCL 16 - 1961
NCl 16 back
NCL 55 - 1967
NCL 55 back