By Julian Linden

NEW YORK (Reuters) - One of the most exciting and unpredictable seasons in years is set to climax with a classic showdown between two of the NFL's traditional giants after the Green Bay Packers and Pittsburgh Steelers booked their places in the Super Bowl.

After a wild season where hardly anything went according to the script, it is perhaps fitting that two of the game's most successful franchises emerged to restore a touch of nostalgia to North America's biggest annual sporting event.

Few teams are more synonymous with the traditions of the Super Bowl than the Packers and Steelers, who each play old-fashioned brands of football built around tough defense, and their showdown is looming as a battle of the ages.

Despite their pedigrees, both teams struggled at times during the season and it was anything but a foregone conclusion that either, let alone both, would make the 45th Super Bowl.

The Packers lost three of their first six regular season games and snuck into the playoffs as the lowest seed in the NFC before reeling off three straight wins on the road against Philadelphia, Atlanta and Chicago with quarterback Aaron Rodgers in superb form after finally emerging from the shadow of his predecessor Brett Favre.

The Steelers began the season without starting quarterback Ben Roethlisberger, who was suspended four games by the NFL for breaching NFL rules on player conduct after he was accused but not charged with sexual assault.

"We're just a bunch of resilient guys," wide receiver Hines Ward said. "Some people gave us a chance, some people didn't, but the guys in this locker room stayed together and believed, and here we are, going to the Super Bowl."

The Packers and Steelers are also two of the most popular and well-supported teams in the NFL and their clash has ensured next month's Super Bowl will among the most watched single-day sporting events held on U.S. soil.

About 100,000 people will fill the state-of-the-art home of the Dallas Cowboys to watch the game live while an estimated worldwide audience of over 100 million will view the televised broadcast where advertisers pay an estimated $3 million for each 30-second slot.

The teams will remain in their home cities for the first week before traveling to Texas on Sunday for a week of frenzied media commitments and promotions for what Americans call the greatest show on earth.

(Editing by Frank Pingue)