In my experience, aside from the keys mentioned, it's all about the grade on Canadian priced books.
I buy high grade Canadian copies for runs that I've already finished, just to give me another reason/excuse to collect more copies of that title. Most are few and far between in high grade IMO.
If people are just trying to complete a run, they might chose American over Canadian, just for uniformity sake.
So it's really just a tiny sliver of the total Market (like me) who care about (and bid on) odd books like variants, double covers, Mark Jewelers, etc.
I just paid about double GPA for a Canadian CGC 9.4 White copy of Wolverine LS #3 because I've been looking for one for years to complete my Wolverine LS (all American direct <1-4> all American newsstand <1-4> and all Canadian newsstand <2-4> versions) set.
As far as these books being called variants - that battle was fought (remember Joe Collector?), and has ended, with CGC now noting 'Canadian Price Variant' on the label (previously noted on labels as 'Canadian Edition').