Since you're going to the Grand Sirenis Mayan Beach - they have a dive rep on the property. I'm not sure which dive op is running it though but it is a PADI center. A quick call to the hotel and they should be able to give you a number to the op.
You are located an hour or so from Cancun. But, there are some pretty good dives right in that area. I can't remember the name - but there is a grassy flat down there that's full of turtles. Shallow drift dive.
A few reefs are also down that way. None of the dives seemed to be to deep - maybe 60-80 foot max. I'd have to pull the log book to actually see.
Cenotes are close by as well.
If you're new to diving and/or new to Mexico - I'd stick with the dive op on the property. They'll look after you pretty well down there.
Just my 2-scents worth - YMMV.
Added info - this is what has been posted on TripAdvisior:
"....The dive staff were friendly, helpful, and very careful about safety. The divemasters know the area very well, and were great to find and point out sea life that you would otherwise miss. The prices for diving were comparable to other dive centers he has used. He did have a night dive booked and paid for, but had to skip it to accompany me when I went for stitches. Anna at the dive center cancelled the credit card payment for that dive immediately, with no hesitation, which was much appreciated......"
You are also near Playa del Carmen. You could always take a taxi or collectivo to the ferry and go to Coz and dive there as well. Just depends on what type of adventure you're looking for.