MEGS, the $18 would have to be worth it..In 05 we were on Carnival Spirit, Hawaii to Vancouver then Alaska. In Vancouver we had to go through Canadian and US Customs/Immigration. There were 3 ships in port and I tell you it took us Aussies 3 hours to get back on board the ship after getting off and having a day in Vancouver, we had to go through the lot (again.) So did every every other passenger irrespective of passport staus. So as a US citizen if you have the chance to bypass thousands of cruise pax at Vancouver terminal, GO FOR IT.
The US Border Security have to check every one in Vancouver enroute to Alasaka as there are no such facilities at the cruise ports in Alaska, Skagway, Ketchikan etc. But at Vancouver there were nowhere near enough officers to check the 5000 cruise pax of 3 ships.
Best wishes from OZ