Even though Sydney is so anti Broncos, I think we will all be surprised how many Broncos fans will be there. I mean actual fans, not neutrals going for Brisbane.
It goes like this in Sydney SLR. People in Sydney hate Brisbane for a number of reasons which are:
1. Success. Brisbane is the most successful and well run club in the NRL hands down on and off the field going as far back as 1988. You have the Broncos at number 1 then there's the rest.
2. Rivalry. it was always good to hate Allan Langer, Michael Hancock and Gordon Tallis.
3. Queensland. When you think of the Brisbane Broncos you really tend to think of QLD as they seem to represent QLD far more then what the Cowboys do if that makes sense. Hating the Broncos goes hand in hand with hating QLD whereas the Nth QLD Cowboys are just some team, that plays somewhere far up north, detached and far away from reality and they're just some team that never really beats anybody (well not the first 20 years anyway).
So to answer your question YES the Broncos do have more supporters then the Cowboys in Sydney hands down and that's obvious when you talk to people and when you go to games. You always see far more Brisbane supporters then you do Nth QLD but the majority of neutrals this Sunday I'd say will be going for the Cowboys.
People tend not to hate the Cowboys here but they do hate Brisbane.
I remember going back to 2004 when the Cowboys beat the Dogs in the finals after sneaking into the 8 in 8th position or something like that from memory. The state of NSW really got behind the Cowboys that year and I remember even when I went to the Cowboys v Roosters game at ANZ there was a hell of a lot of Cowboys supporters there that surely had to be a good chunk of them from Sydney.