In the left corner will be Mr Brown, with widespread support, eye-balling the Government on issues like affordable housing, leaky housing compensation and inner city rail.
In the right corner will be the current Minister for Building and one-time Transport Minister. It's the sort of popularity contest a year before a general election that makes governments nervous.
Especially when your candidate is a known maverick.
Rather oddly, Labour's Auckland spokesman, Phil Twyford, is hoping Mr Williamson won't stand. For a party finally staggering to its feet after its 2008 defeat, you'd have thought the chance to get in behind its de facto candidate Len Brown, and give National's representative a bloody nose, would be irresistible.
Mr Williamson's parliamentary career has hardly been stellar, but the instant celebrity status he attracted after his gay marriage speech suggests he won't be a pushover.
He has that outspoken quirkiness that we voters seem to prefer in our local leaders. And he speaks in sentences of plain, easy-to-follow, English, which is a definite point of difference, even if you don't agree with what he says.
His big handicap is the ministerial baggage of someone who entered parliament in 1987. Whenever he or his National colleagues talk of the need for tolls or public private partnerships to fund more road building in Auckland, he'll be leaving himself open to questions about what did he do about the problem when he was National's minister of transport for all but one year between November 1993 and November 1999.
Over that period, only 25 per cent of national road builder Transit New Zealand's money was spent north of Pukekohe, despite that area being home to around 40 per cent of the country's population.
In 2009, the Greens' transport research unit analysed years of Cabinet and Treasury documents and calculated that between June 1990 and June 2005, Aucklanders paid $7022 million in fuel taxes, road user charges and licence fees, but got only $3321.94 million - less than half - back in transport-related spending.
Not that Mr Williamson doesn't like motorways. Before the 2005 elections he was comparing them to arteries in your body, pointing to Auckland's unfinished highways with the comment, "if your arteries don't join up you'd be dead".
He said that if we listen to people who don't want motorways, Auckland would build no more - "and we are grossly short of them".
Before the 2008 election, Mr Williamson embarrassed Mr Key by pushing for road tolls of up to $50 a week to pay for his highway building plans. He said he didn't know anyone who would not pay a $3-$5 toll each way if it would save them 40 minutes of commuting time.
On this, the two mayoral candidates seem on common ground. Mr Brown recently declared his conversion to tolls and other forms of road pricing. But they differ markedly on the need for public transport. In 2003, Mr Williamson asked in these pages "If congestion is as bad as we are told, and public transport such a great alternative, why aren't people just moving that way of their own volition?"
It promises to be a lively debate. And when they tire of transport, there's also the up-to-$20 billion leaky home bill, and who should pay. City or state? Seeing the Housing Minister squirm his way around this will be worth the ticket alone.
