The company plans to make its parks Disneyland's main rival worldwide.
Legoland is the third most popular tourist attraction in Europe, where its parks pulled in 5.6 million visitors last year.
The review is being handled by the AAR, which has drawn up a shortlist of five agencies to pitch for the brief. The contenders have yet to be named.
The private equity firm The Blackstone Group bought the theme parks for EUR375 million in July, prompting the pitch.
The agency search does not affect the pan-European Lego account, which is handled by Rainey Kelly Campbell Roalfe/Y&R.
Blackstone also owns Merlin Entertainment Group, which owns the Sea Life Centres. These will be merged with Legoland parks. The Toy giant Lego was forced to sell the theme parks after a disappointing set of results in 2004, when it lost £37.2 million.
In the UK, Legoland has concentrated on promotions to encourage people to visit its park in Windsor. Its most recent work was a door-drop campaign to homes within two hours' drive of the park. The work, by Circular Distributors, was sent to 1.2 million families with children aged three to five.