There is some similarity between the Thomas de la Rue Design X III (see attached) and the Bradbury Wilkinson $20 essay.
In 1903, Bradbury Wilkinson and Company was acquired by the American Bank Note Company. In 1917, it moved to New Malden in Surrey still operating as Bradbury-Wilkinson as a wholly owned subsidiary of ABNC. Coincidentally in 1986 Bradbury-Wilkinson was acquired by De La Rue but that was long after the design of the 1969 Bank of Canada $20 note was finalized.
The $20 essay that I posted is from the Estate of Derek Friday. Mr. Friday was an artist who in the 1950s left the RAF and began as an apprentice in the design department of Bradbury Wilkinson working there for almost 30 years hand drawing and painting the designs for banknotes, share certificates and debentures.
Here is a link to the October 2021 Bank of Canada Currency Museum Blog you mentioned:
https://www.bankofcanadamuseum.ca/2021/10/moving-mountains/