Hmm I have taken the ferry a lot from Seattle and did not get checked as much as at the peace arch but maybe I just got lucky.

my family lived in BC but worked in the US so we had to cross the border everyday and deal with those guys 2 and 3 times a day. So I can tell you they can be assholes.

My son got a misdameanor in the US and the canadians would not let him cross the border to get home. We had to pay someone to take him on a boat. I guess it will just depend on the person you get.

The main crossing Peace Arch is the worse...As you drive east you'll hit the truck crossing....keep going east and you will hit the surrey crossing. It is small kinda out in the country. With passports they should be ok. The hassles are usually over a birth Certificate not being clear enough...they have to be able to read every word...they will run your car plate in their computers and check for warrants from whatever state it is from. Your friends could try crossing at the main crossing and if it does not work wait an hour and go down to the surrey one.
Good luck...
Cat