Hi,
Went through your post here and what you need is a app which will download music from your library which you will manage.
You need the in-app purchase feature for users to purchase your content.
We can design , develop and deliver this app for you.
We have e representative in Canada as well who could server as a POC for you if need be.
Please read your PMB for our details.
Cheers,
Rahul.