Thanks so much to all who responded to my customs questions.
Because of your responses, I contacted my Travel Agent again, and she in turn called Holland American Lines, and Northwest Airlines AGAIN.
This time, she verified that by us using HAL's Signiture Baggage Service (which we sign up for while on the cruise ship), we will NOT to have to handle our checked baggage from the time we leave the ship in Vancouver until we take it off the carousel at Baltimore Washington International.
In Detroit, we will not have to do anything except get off one plane and get on the connecting plane to BWI.
And we will not have to go through any customs inspections with the possible exception of our carry-on items at Vancouver.

Thank you so much for your assistance in hepling me get the facts straight about all of this.

Ed