That's the app developer's fault. They thought they were being smart by saying "oh, if you're in en_GB, lets give you Yelp.co.uk by default". And yeah, sure, that works for most users.
On the other hand, I don't think its fair to fault app developers for that, since there isn't otherwise a way to query the OS for "what country is this user in?" without asking for (and getting) full-precision location access.
And the stubbornness in refusing to add en_CA is confusing. How long could it take? At the risk of talking ill about my own employer (Android is a different team which I have no connection to tho) it seems rather culturally insensitive. I'd put the change together myself if I knew anything about it.
I should note that this is in stock Android on a Nexus. Motorola and others ship their Android with an en-CA locale.
And switching to en_GB means getting dinged for words like organize, getting odd keyboard layouts, getting news and weather from the UK, and navigator speaking in English accent and dialect.
It's worth nothing that other manufacturers (such as Motorola) ship their Android with an en_CA locale. It's stock Android on Nexus that has the problem. That Google hasn't bothered is rather awful.