I suggest you e-mail the hotel directly, asking availability to use your suite upgrade certificate. If the hotel is customer friendly, it should respond promptly and confirm the suite if it has availability.

I used my suite upgrade certificate at Hyatt Regency Osaka by e-mailing the hotel asking for availability. Hotel replied in 2 days time and confirmed the suite upgrade. My reservation on hyatt.com also show the change of room description also. (from a regular room to an executive suite).

We checked in very late, like 9pm. Handed the certificate over to the check-in clerk. The suite was ready for us with welcoming amenity. (3 kinds of fresh fruits, banana, strawberry and grape, very nice).