The idea of a Nicaraguan canal has been around since the days of Cornelius Vanderbilt. Not going to happen.
IIRC overcoming the enormous engineering challenges and structural complexities of the Panama Canal was seen as less daunting a task than digging a sea level canal through Nicaragua, even with the available technology of more than a century ago.
What makes the Chinese think they can succeed in Nicaragua now probably has to do with their “success” in re-engineering the Yangtze River, where the concerns of the local populace mean little to the communist bosses in Beijing.