The are represented by different unions. Grand River Navigation is MM&P’s Inland Division. Interlake is MEBA. If you go with the MEBA there is always the option of going deep sea with another MEBA contracted company if you tired of the Lakes (as long as you hold the qualifying license). With the MM&P transferring to the Offshore Division is a bigger hassle.
MMP Inland Division to MMP Offshore - Maritime Employment - gCaptain Forum