His full name is James Derrett McCarthy (1927-1982). A graduate of the Ontario College of Art (now OCAD University), he was a commercial artist whose work could also be seen on other paperback covers and in Canadian magazines
Here are four of his covers from 1952 - all historical fiction.
Harlequin 169 - May 1952
Harlequin 178 - July 1952
Harlequin 187 - September 1952
Harlequin 190 - October 1952