Update on the AM hotel booking site.
1) I found Pop Century today, for my dates so they might be adding more availability for others too.
2) I learned it is, in fact, as simple as they said about cancelling. In fact, my 24,000 AM were back in my account after only 20 minutes. ***ETA - they are in my Airmiles.ca account, but not yet visible on the travel hub (so not yet available to re-book with). They did say within 24h, so we'll see.
*** ETA also - now approx. 1 hour after cancelling online, they are available to book again.
3) There is, however, a $10 NON-Refundable booking fee associated with every booking, so technically cancelling wasn't "free" for me, it was "free from the hotel side of things, but $10 from AM hotels website". This is the 7th question on their FAQ page, which I didn't recall reading before booking, but it's there!
I plan on using my AM now for the best bang for my buck, and now that the discont tix are up online, I don't know what that is!
If my math in my spreadsheet is correct (and assuming 1.35 exchange rate) the hotel rooms are approx. 12 cents per AM, the discount WDW tix are 11 cents, and Universal for a day are only 10 cents per AM.