Women’s football is the first event of the Olympics and is to kick off later, two days before the official opening ceremony.
The Team GB women’s football side will get 18 days of sport under way at 16:00 BST against New Zealand at Cardiff’s Millennium Stadium.
Designated Games Lanes, covering about 30 miles of roads and off limits to the public, have begun operating in London.
And government lawyers will go to court to try to stop a public sector workers’ strike on the eve of the Games.
Culture Secretary Jeremy Hunt will join Welsh Secretary Cheryl Gillan in Cardiff for the first event of the 2012 Games.
Team GB coach Hope Powell said opening the Games was a “great honour” and would hopefully give people “a greater appreciation of how good women’s football actually is”.
And captain Casey Stoney said she hoped the fixture could “raise the profile of women’s football”.
“It’s a global thing, not just for our nation, and hopefully we can put on a good show – but we are just focused on getting the job done.”
Team GB drew 0-0 against Sweden in their final warm-up fixture at Middlesbrough’s Riverside Stadium last Friday.
Relative unknowns Cameroon and heavily fancied Brazil will take each other on at the stadium after the GB game, and four other matches in the same competition are also taking place later in the day at Hampden Park in Glasgow and the City of Coventry Stadium.
The Olympic Route Network (ORN), made up of 175 miles of roads connecting up the main Olympic venues across the country, comes into force on Wednesday.
It is designed to make it easier for athletes and officials to get around the Games and has seen junctions blocked off, bus stops moved and parking bays suspended.
As part of the ORN, the designated Games Lanes in London will be in operation between 06:00 BST and midnight and only open to VIPs, athletes and accredited media.
Ordinary motorists going into the lanes face fines of £130 ($205).
Mark Evers, Transport for London’s (TfL) director of Games transport, said commuters must leave more time for their journeys.
“The worst case scenario for us is that people try to chance it and, those first few days of the Games, that they try to do what they ordinarily do – and I can guarantee all people that travel around London, those first few days of the Games are going to be really busy,” Mark Evers said.
“It’s vitally important that they come up with a plan that takes into account the busy parts of the network.”
TfL commissioner Peter Hendy said the early signs were positive: “We’ve seen a marked reduction in road traffic in the last 10 days, which is along the lines of what we asked Londoners and people who work in London to do.”
In the High Court, the government is to argue for an injunction to prevent public sector workers, including immigration and passport workers at Heathrow and other airports, taking strike action on Thursday.
Thousands of spectators are expected to arrive at Heathrow Airport on that day.
The Home Office says it believes there was a “procedural error” in the ballot of members of the Public and Commercial Services union.
But the PCS said it was “confident” the strike was legal and would happen.
The government insists contingency plans are in place in the event of industrial action.
