If your occupation appears on the list below then you can apply for the federal skilled worker program (assuming you have the 67 points to qualify):
http://www.cic.gc.ca/english/immigrate/skilled/complete-applications.asp
If your occupation does not appear on this list, then you need a job offer in Canada to apply through the federal skilled worker program.
Seaman is not an occupation that appears on the federal skilled - so you'll need a job offer in Canada if you want to apply.
