Not really Brett. The league winner gets invited to B3, and the cup winner gets invited to B3. So some years it's two teams, but other years it's only one. Also, previous winners of B3 get a perpetual invite - Australia doesn't have any (yet), but if we did it could be more than two.
Both of those things (winning the league and winning the cup) have a huge influence on your ranking, so it's usually very highly ranked teams that participate - but that's only an effect of qualifying, not the cause of it. :)