In 1957 the United States Tariff Commission examined the distilling industry chiefly from the standpoint of whisky, the main spirit at the time. The issue was how tax or tax-related changes would affect the various players in the U.S. market. These were mainly American and Canadian companies, in some cases with interlinked ownership. Scotch whisky imports was the third variable.
The investigation was comprehensive, covering such things as product types, production methods, sales channels and data, names of large industry members, and ownership details. Extensive data was sourced from distillers to support the statements in the study. Many interesting statements are made especially regarding the new charred barrel for bourbon and straight rye, e.g., its use became mandatory only in 1938. The effects of the charred barrel on the spirit vs. used barrels was considered, also national preferences for spirits and how they arise.
The statement was made that the new charred barrel only became an industry practice for bourbon and straight rye – vs. something legally compelled – in the second half of the 1800s. This is consistent with the arguments Hiram Walker successfully made in 1909 that a grain distillate composed in part of a light-bodied, almost neutral whisky was entitled to the appellation whiskey no less than straight bourbon or rye.
The first paragraph in the page reproduced below (from HathiTrust) states the nature of the distillates in the typical bottle of Canadian whisky.
Today, the explanation is still generally accurate except that the high end of the range for light-bodied whisky is probably typical, i.e., 94% abv. The percentages of each whisky type used for the blends was not stated on this page. IIRC the study elsewhere states about 1/3rd heavy whisky was used. Some Canadian blends today would match or exceed that. I’d think for the bulk of production the percentage is rather lower, based on various gleanings over the years. The strip stamp system mentioned is not currently used but many older readers will recall when Canadian whisky bottles bore the stamps. Canadian whisky is still of course bottled under Canadian government supervision.
In other parts of this study, one may find statements concerning the permitted use of flavouring in Canadian whisky (very similar to today’s rule for exports, the 9.09% rule) and many other interesting observations on the industry as it then was, and still in many cases is.