a) Chain stores – national such as Woolworth, Kresge, Metropolitan and Zellers; regional such as Stedman’s [sic] and Beamish; United Cigar Stores; railway station stands run by The Canadian Pacific Railway News Department and The Canada Railways News Company.
b) Other retailers – in smaller cities and towns through drugstores or general stores.
c) Newsstands – where they were introduced by wholesale news dealers who handled paperbacks along with magazines.
Here is something from Christmas 1943 that doesn't mention paperbacks but is about the magazines that would have been sold along side paperbacks in 1944. It's interesting to note that almost half of the adult magazines (17 of 39) are still published nearly 70 years later.
Most of the paperbacks would have been the Canadian editions of Pocket, Avon and Dell, among others. The only Canadian publisher was Wm. Collins & Sons Co. Canada Ltd with their White Circle imprint. Here are a couple of White Circles that might have been on the shelves that Christmas.
White Circle 90
White Circle 99