Alright, I'll give it a try...
Beats
Available on iOS, Android, Windows and Web.
HOLD UP. BEATS MUSIC IS NOT YET AVAILABLE IN YOUR COUNTRY.
So... Beats doesn't support OS X and I'm going to take a wild guess that it probably requires Flash for the Web version. Anyway it's not available in Canada.
Spotify
Spotify works on your computer, mobile, tablet and TV.
Spotify is currently not available in your country.
Not available in Canada either, nor can I see any technical details about "works on your computer".
iTunes Store
Allows me to buy music in Canada. Works on my 2010 Mac mini, my old 12" PowerBook G4, my iPod shuffle, my old iPhone 3GS and my 3rd generation Apple TV.
Winner: iTunes Store (Canada).