Second attempt at calling took me 2 hours 20 minutes on hold, but then I got through. As someone else mentioned, the agent couldn't find a record of me being sent the offer so I had to forward the email, but that was the only hiccup.
My first choice sailing still had availability, and I got booked into a nice 2B on deck 7 for $284US of taxes and fees. Interestingly, after initially asking if I wanted to be charged in US or Canadian funds, he then backtracked and said casino offers can only be paid for in USD.