Boston Properties and Brookfield Financial Properties, two of the largest commercial landlords in New York, have joined forces in making a multibillion-dollar bid for the World Trade Center, the 10.6 million-square-foot complex in Lower Manhattan. The two real estate giants, as well as Vornado Realty Trust and Silverstein Properties, will submit their final offers today to the Port Authority of New York and New Jersey, which owns the complex. The bids for a 99-year lease are expected to reach $3 billion. A final deal is expected to be negotiated by the end of the year. In 1998, the Port Authority was hoping the complex would fetch $1.5 billion. But its value soared because of the rising real estate market and better management of the complex, where revenues rose from $317 million in 1996 to an estimated $371 million last year.