Sir Brian said the All Blacks faced no easy task.
The Australians seemed confident, boosted by their Waratahs Super 15 side's win in the final against the Crusaders a fortnight ago in Sydney.
Sir Graham Henry, who is in Sydney for tonight's match, said the "greatest team of all time" accolade was "a bit of stretch".
"But you could say it's the most successful side in games won in succession of any one nation in the history of the game."
Sir Graham, who was All Blacks coach from 2004-2011, said he thought the All Blacks were a brilliant rugby side and would be too strong for the Wallaby team, which had a number of key players missing due to injury problems.
All Black forward from 1995-2000, Josh Kronfeld, said to call a current team the greatest was a "massive comment" and something best left to history to judge after a few years had rolled by.
However, it could be said that a team was one of the best in the world at a particular time in rugby.
"They would be a wonderful team to be involved with and play with.
"They have a great sense of where they are and what they do on the field, and impose their dominance."
He did not believe the Wallaby forward pack was equal to that of the All Blacks, and it was questionable whether the current team had the technical skill level needed to win.