Google’s John Mueller in a webmaster hangout earlier this month said at the 8:30 mark into the video that just because you rank well in one Google regions, it does not mean you will rank well in another. So if you rank well in Google Canada for your query, it doesn’t mean you will rank as well in Google US for that query. John said the “that competition is very different across these country versions.”
Here is the video embed:
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Transcript:

The biggest thing that I sometimes see in cases like this is that a site will kind of look like this in the sense that they rank in one version of Google or one country domain, therefore they should rank the same on all others or on .com, the US. And in general, that competition is very different across these country versions. So that is something where it would be completely normal where we would have very different rankings in these different country versions.
So a site might be completely fine and good in rankings in Google Canada because there are fewer other sites that are competing for these queries on Google Canada. But because the competition is so much stronger in the US, maybe it would be ranking very differently.
So from that point of view it is kind of normal that you would see this kind of difference. It is not something that I would call out as a bug on our side or a bug on your side, not something that you are doing something wrong.

Hatip:

Via @johnmu: The competition is very different across Google country domains. Normal to see fluctuations across them https://t.co/8ODZZnsFqU pic.twitter.com/jevlqKatrt
— Glenn Gabe (@glenngabe) September 28, 2017
Of course, this is a very obvious point to many but to others, not obvious at all.
Forum discussion at Twitter.

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