This is very helpful, Trevor. Your suggestion that I use (?s).* as the find what parameter was the key for me getting Jongware's Find/Change suggestion to work properly.
Thanks to you and Jongware, I now have several methods of changing text language to English Canadian based on various circumstances: when the text has paragraph and character styles applied (with the option to reformat existing styles), and also the ability to use Find/Chage to apply the change to text that is unstyled, or partially-styled.
Many thanks to you gentlemen for your kind assistance!