The 12, 782 dwt freighter BBC Steinhoeft became stuck in the St. Lawrence Seaway in Montreal, Canada becoming the first accident of the shipping season which opened on March 23.  The freighter had left Toronto, Ontario bound for Philadelphia, Pennsylvania with a cargo of mechanical parts when it became stuck.   Five other vessels were delayed while the Seaway was blocked.    Tugboats were able to unwedge the vessel later the same day.   No injuries or pollution was released.  Government and St. Lawrence Seaway officials are investigating the incident.  No statement has been released to the cause of the incident.