Moderator, Marriott Bonvoy & FlyerTalk Evangelist
Join Date: Oct 2002
Location: McKinney, TX, USA
Programs: United Silver; AA Plat/2MM; Marriott LT Titanium; Hilton Gold
Posts: 11,727
I've not stayed at the Cancun RC, but the Cayman RC offered a 'per night' cash upgrade to their club level if I wanted it (this was a few years ago and well before the "Bonvoy" program merge though.)
My guess is it is up to the hotel to decide what they will or will not allow. You might try to see if you can contact the GM directly to see if this is just that one person's decision or the hotel's decision.) Another option is to wait and try to upgrade when you check-in.