PCL and Oceania (and another that is escaping me right now) don't even allow US or Canadian agencies to book forign nationals on their cruise ships unless they have a US or Canadian address.
Don't know the reason for sure but am told it's financial. They get higher rates from overseas agencies. This even applies to the online booking agencies based in North America, which 99.99% of them are. Some agents here get creative and break out a phone book for sizable bookings and give them an address. If such cases are caught the commissions are withheld from the agent and agency.
Hurts when you get a call for an Oceania Suite, those are big $$$.