Kolkata, Feb 27 : The Communist Party of India-Marxist (CPI-M)-led Left Front, Congress and Pirzada Abbas Siddiqui's Indian Secular Front (ISF) will organise a mega rally in Kolkata's iconic brigade parade ground on Sunday. The three-party electoral coalition is slated to launch its poll campaign from the mammoth rally in order to mark the beginning of their canvassing for the forthcoming state Assembly elections. Left front chairman Biman Bose went to the parade ground on Saturday afternoon to take stock of the preparations. He said: "This will be one of the biggest brigade meetings ever. As far as the estimates we are getting, the entire brigade ground is going to be choc-a-bloc tomorrow." The Left Front and the Congress have already finalised the seat-sharing agreement. Talks between the Left and ISF have also been sealed as both the parties have agreed upon 30 seats for the newly-floated political outfit. Sources, however, said that the seat-sharing negotiation between the Congress and the ISF is still underway. "The coalition is to offer an alternative to the anti-people and communal politics of the Trinamool Congress and the Bharatiya Janata Party (BJP)," said senior Congress leader Pradip Bhattacharya. /IANS