Kobo originally offered me Styles and Secret Adversary for free, even though they aren't out of copyright here in the UK. They were the first Christie books I'd read, and I enjoyed them enough to collect the whole set (albeit mostly in used pb, which still doesn't give HarperCollins any money). I'd probably never have read any of her work if they hadn't made that mistake.
Anyway, I was going to say that I'd made a spreadsheet of how the Complete Stories collections map to the original (UK) canon, which is
here. I don't know how much use it is in Canada, or even if the contents are exactly the same, but I've been using it to track my reading.