To migrate a 1 TB PostgreSQL database from a Compute Engine VM to Cloud SQL for PostgreSQL with minimal downtime, the best approach is to use the Database Migration Service (DMS). DMS is designed for minimal downtime migrations by continuously replicating changes from the source to the target database until the cutover is performed. This ensures that the target database is up-to-date with the source at the time of cutover, minimizing downtime. Option A would involve significant downtime during the export and import process. Option B, Migrate for Compute Engine, is not suitable for database migrations as it is designed for VM migrations. Option C, Datastream, is a change data capture and replication service but is not specifically designed for database migrations like DMS is.