Daid - I don't know where you were looking on the HAL website, but I found 4 Amsterdam sailing to Canada/New England for 2006.
Thu Sep 7, 2006 10 Eastern Canada & New England: New York to Montreal 10 day ms Amsterdam
New York, New York to Montreal, Quebec
Sun Sep 17, 2006 10 Eastern Canada & New England: Montreal to New York 10 day ms Amsterdam
Montreal, Quebec to New York, New York
Wed Sep 27, 2006 10 Eastern Canada & New England: New York to Montreal 10 day ms Amsterdam
New York, New York to Montreal, Quebec
Sat Oct 7, 2006 10 Eastern Canada & New England: Montreal to New York 10 day ms Amsterdam
I also found 17 sailings on the Maasdam, plus a 15 day sailing from FLL to Montreal.
Montreal, Quebec to New York, New York
Go into HAL's website, click on Destinations, Canada/New England and then click on "View all for Canada/New England.