Dorothy Dumbrille's All This Difference was published by Harlequin in 1963 as number 718. By this time (starting in 1960) all but a handful of Harlequins were romance. This was, in fact, the last non-romance fiction Harlequin published. What makes it unique is the header on the front cover. It is the only time Harlequin marked a book as Canadian in this way. Another Canadian novel, Peace River Country by Ralph Allen, was published at the same time by Harlequin as number 706 without the tag.
Thanks to the artist, Bern[ard] Smith, who was responsible for many of Harlequin's romance covers at the time, the book looks like a classic Mills and Boon Harlequin romance. But the story revolves around French/English, Catholic/Protestant tensions during the second world war in Glengarry County, Ontario. Glengarry County is east of Ottawa on the Ont/Quebec border.
It's interesting to note that the cover image is clearly early 1960s, not early 1940s.
Dumbrille (1897-1981), largely known as a poet, had this novel published in 1945 by Progress Books of Toronto.