As about 100,000 Argentines poured into Rio de Janeiro, a record global television audience of several hundred million is expected for the finale of the 20th tournament.
The game starts in the historic Maracana Stadium at 4:00 pm (1900 GMT) in front of 73,500 fans but under an unprecedented international spotlight.
With national excitement mounting after their country's 7-1 demolition of Brazil in the semi-final, up to 200,000 German fans were to pack a fan zone around the Brandenburg Gate in central Berlin. Millions more were to huddle in front of screens in beer gardens, bars, sports clubs and homes across the country.
On top of huge numbers heading for Brazil, tens of thousands of Argentines were expected to pack the Plaza San Martin in Buenos Aires.
The football fiesta has turned into a global party with World Cup events organized in virtually every country. One Bangladesh farmer made a 3.5 kilometer (2.2 mile) long German flag which is surrounding a stadium in the western Bangladesh town of Magura.
Germany start as favourites to win the trophy and become the first European side to win a World Cup in the Americas.
A victory for Argentina would give its captain Messi his first World Cup and elevate the four-time world footballer of the year among the game's greats such as fellow Argentine Diego Maradona and Brazil's Pele.
The final will be "the most important match of our lives for our country," Messi wrote in an eve-of-final call to arms on Facebook.
"My dreams and my hopes are being fulfilled due to the hard work and sacrifice of a team that has given everything from match one.
"We knew it was possible. Our people, the Argentines, they have carried us here. But the dream is not over yet. Tomorrow we want to win, and we are ready!"
Argentina's coach Alejandro Sabella said the South Americans will have to produce "a perfect match" to overcome the talented Germans.
"Germany are always very strong physically and tactically. For that reason they are the team that has won most titles along with Brazil and Italy.
Germany coach Joachim Loew believes his team is ready to claim a place in history as they attempt to end a run of four major tournaments where they have reached either the semi-finals or the final only to fall short.
"Regardless of what has happened in the past, it is a matter of winning now and we know we can write history, because Latin American sides have been able to dominate on home soil," said Loew.
Brazilian authorities are preparing their biggest ever security operation for the final with about 25,800 police, soldiers and private security guards on duty in the city and at the Maracana.
Russia's President Vladimir Putin, whose country will host the 2018 World Cup finals, will join Brazil's President Dilma Rousseff for the game.
In a bid to avoid violence, bars around the Maracana stadium will be ordered to stop selling alcohol two hours before Sunday's match. Police blockades around the stadium were in place on Saturday.
Swathes of Rio were transformed into a miniature Buenos Aires on Sunday, as cars and buses packed with Argentine fans waved their country's white and blue flag and honked their horns.
For Brazilians, despite their side's thrashing by Germany, they want the Europeans to win rather see rival Argentina take the trophy and add insult to their injury.
Brazil is basking in the glow of one of the best World Cups in history despite the 7-1 defeat and a new 3-0 reverse in the third place playoff against Netherlands.
Brazil captain Thiago Silva issued a new apology to the nation after Saturday's defeat through a penalty by Robin van Persie and goals by Daley Blind and Georginio Wijnaldum.
"It is a moment of great sadness, because we tried everything and didn't get the outcome we dreamed of. It is difficult to go home and say to your family: 'Sorry, I didn't manage it'," declared Silva.
Coach Luiz Felipe Scolari said he was leaving his fate up to the Brazilian federation.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ