Welcome to the cruisereviews.com message board! Sounds like you've already done a lot of research, which is great. If it were me, and a passport wasn't an option, I'd go with the passport card. You will need to mail in your certified BC to get one, so it's good that you have some time. Also, even if you have the passport card, bring your BC and DL as back-up, just in case.
Another consideration is how often you will use it. If you take a lot of cruises into and out of the U.S., it may be worth it. If you live near a border crossing and frequently travel by car between countries, it may also be worth it. (In fact, the latter was the original intent.) Yet, if you do a lot of flying, the passport is the better option. In my case, for instance, I fly with a passport even domestically in case there is a cancellation and there's a chance for a re-routing through Toronto. (I live in the Northeast U.S. where there are several such flights a day.) Of course, I'm digressing as a passport is not possible for you now, but something to consider for the future.
The cruise line doesn't matter... you'll be dealing with the Department of Homeland security, which oversees everything.