I have a Canadian cell phone and a US cell phone, each with a corresponding Apple country account.
I checked and can confirm that searching the app store on the Canadian phone/Canadian app store account there is no app for Best Friends Pet Hotel.
Searching on the US phone with the US app store, the app is there.
So it appears the app is only available on the US app store (and by extension only to US guests).
I would suggest writing to Best Friends and requesting that they add it to the Canadian (and other international) app store, since only their US guests will be able to access and use the app as it is now.