The fact that you've got a language selection at all implies that it's an international site. If it's a store or some such it would be a very unusual American website that shipped abroad but not to Canada.

(I'm not sure what "meant to be consumed primarily in the US" even means; I don't have national borders in mind when writing. For most sites it makes very little difference which country a visitor happens to be from.)

The US and Canada have the primary language of English. But Canada also has French, and certain sections of the US have Spanish as a predominant language. Just one example: If I have a US company that also ships to Canada, it makes sense to have the US flag for English and the French (or Canadian?) flag for French Canadian. It also makes sense to have the Mexican flag for the Spanish option, because most of my Spanish speaking customers are likely to hail from Mexico, with a small number from other Central American countries.

What would not make sense is to have a UK flag for American customers, a Spanish flag for Mexican customers, and the Democratic Republic of the Congo flag for French, just to appease people who will never buy from my site. You might not have national borders in mind, but it pays to know what language your customers speak as well as what countries they are from.

In those instances I'd probably suggest going for a American/British flag [1] or maybe the same thing with the American/Canadian flag?

[1] http://thecultureur.com/wp-content/uploads/2012/12/e7qd6.jpg

However I can forgive the use of the American glaf in your example as if you're shipping software then that's a little different as it's a targeted application rather than my example example of a public facing website which would have people from all nationalities visiting.

If you've got different language options then it's not aimed primarily at the US

I had this discussion recently due to the Coke commercial during the Super Bowl, but I'll give you the highlights.

Not everyone in the US speaks English as a primary language.

I appreciate what you're saying but number of public websites with different language options which weren't meant for countries outside of the US is going to be pretty low relative to the alternative. Occam's Razor would suggest those sites are generally intended for international consumption.

However, to get back to my original point, I was commenting about how all countries nationalise common language; and regardless of the justification of using an American flag for English language options, it's still an example of that point.