Localization for Canada defaults to UK; should default to US

I'm working on an application that has localized strings for the UK, specified in res/values-en-rGB/strings.xml. My default string implementations, for the US, are in res/values/strings.xml.

Now, I'm adding additional localizations for Canada in res/values-en-rCA/strings.xml. I would like the application to behave as follows: If a user's device is localized to Canada (or their language is set to English(Canada) or French(Canada)), check if we have a string in en-rCA, and if not, fallback to the string in my default strings.xml file. However, my application currently fallbacks to strings from en-rGB when the device is set to a Canadian locale and the string is not found in en-rCA. Therefore, I have two questions:

1. How can I configure my app such that a device with a Canadian locale searches for a string in en-rCA and then, if it cannot find it, defaults to the string in my default values folder rather than en-rGB?

2. How can I ensure that a device whose language is set to French (Canada) defaults to en-rCA rather than my default values, as it currently does?

I would be happy to provide an example if it would be helpful. Thanks!