Restore music library after changing App Store regions

There were some steps you should have taken before switching regions:

To make sure that you can access your previous purchases in your new country or region, redownload your previous purchases on every device on which you might want to view the purchase before you change your country or region.

Back up your iPhone, iPad, or iPod touch to iTunes. You might need to temporarily downgrade your iCloud storage until you switch to the new country or region. You won't lose any iCloud data in the process. After you change your account to a new country or region, re-enroll in a new storage plan to continue using iCloud storage.

Change your Apple ID country or region

https://support.apple.com/en-ca/HT201389

Regarding the Apple Music subscription, you don’t usually get this back once cancelled due to a region switch. The above notes are for iTunes purchases

Apple Music Terms 

Manage your Apple Music subscription - Apple Support 

If you cancel Apple Music, you'll lose access to the Apple Music catalog, any music that you added to your Library, and the features of Apple Music when your current subscription period ends.( this may include up to 30 days depending on the billing cycle and when you cancelled)

If you cancel during your trial period, you’ll lose access to the catalog and features of Apple Music immediately.