The first 500 books published by Canadian Harlequin Books from mid 1949 to early 1960 had 489 different covers. Of these eight were either all type or photographs leaving 481 illustrated covers with 294 having identifiable signatures. Another 18 have initials that are not associated with known artists or illegible signatures. I think I have a good guess for three of those books.
Three books in 1953 were signed by "ATR". A likely candidate is Aileen Tyrrell Richardson (1916-2005). She was a graduate of the Ontario College of Art, lived in Toronto and was an active mid-century illustrator for Canadian magazines, including Chatelaine, and books.
Signature - Harlequin 216
Harlequin 216 - February 1953
Harlequin 230 - May 1953
Harlequin 234 - June 1953