Was there a plan to build utica avenue subway line pro?

Yes. It was known as the Utica Avenue Line. Its construction was proposed by the New York City Board of Transportation (BMT) in the 1920s as a part of its Proposed Expansion of Rapid Transit Facilities. Its route would have run from Atlantic Avenue through Cypress Hills, the New Lots Avenue subway line (L train), and East New York to Spring Creek Park in southeastern Brooklyn. The plan also called for a "stub" line to the Canarsie Pier which would have connected with a ferry service to Rockaway Beach. However, the Utica Avenue Line was never built.