(Adds details of Suzano's proposal, Fibria management not involved in talks)
By Carolina Mandl and Tatiana Bautzer
SAO PAULO, March 12 (Reuters) - Wood pulp producer Paper Excellence has made a formal bid to acquire Brazil's Fibria Celulose SA after barging into the company's tie-up talks with another rival, three people with direct knowledge of the matter said on Monday.
According to the sources, who requested anonymity because the matter was still private, Paper Excellence's bid was structured so as to value Fibria at 40 billion reais ($12.3 billion) in a year's time.
Netherlands-based Paper Excellence also offered a break-up fee of 4 billion reais if it fails to finance the deal, sources said.
Paper Excellence, controlled by the Wijaya family, which also owns Asia Pulp & Paper Company Ltd, decided to bid after reports that Fibria was negotiating a tie-up with Brazilian rival Suzano Papel e Celulose SA, the sources added.
According to one of the sources, Suzano's proposal to Fibria shareholders is different, a cash-and-stock merger. The resulting company would own assets currently owned by Suzano and Fibria. But some shareholders would have the option of exiting their stakes and receiving cash.
Paper Excellence has offered a simple cash transaction, in which all shareholders would have the option to sell their stakes, sources said.
Fibria shares rose nearly 4 percent in Monday trading, while Suzano shares fell about 5 percent. That marked the day's biggest gain and biggest loss on the benchmark Bovespa stock index.
Representatives of Fibria and Paper Excellence did not respond to requests for comment. A fourth person, close to Fibria, said the company's board was not planning to meet to consider the proposals anytime soon.
According to the person, who was not authorized to speak publicly about on the matter and request anonymity, bidders were negotiating with controlling shareholders, industrial conglomerate Votorantim Participações and BNDESPar, the investment arm of Brazil's development bank BNDES. Management was not yet involved in the discussions.
Last week Paulo Rabello de Castro, chief executive officer of BNDES, confirmed the talks between Fibria and Suzano.
BNDES and Votorantim Participações SA are controlling shareholders in Fibria. BNDES also has a stake in Suzano. The sources added that BNDES' support would be decisive in reaching a deal.
Paper Excellence acquired Eldorado Brasil Celulose SA last year for $4.7 billion. Fibria and Eldorado both have operations in the city of Três Lagoas, in the state of Mato Grosso do Sul.
BNDESPar, Fibria and Paper Excellence declined to comment.
($1 = 3.26 reais) (Additional reporting by Gram Slattery Editing by David Gregorio and Tom Brown)