Yes, Soriana is in the Kukulcan Plaza about 1KM south of the Westin Lagunamar. It is in the same mall as Ruths Chris and there is also a Harley Davidson store there. You can either walk or take the bus there. There is a La Europea about halfway between Lagunamar and Soriana on the lagoon side of the road. Get your alcohol and wine here and your beer and groceries at Soriana. Each were just fine for us for our recent 13 night stay.
Also, you can have your groceries delivered from Soriana to Lagunamar for only $30 pesos (about $1.50 US$). Be sure to tell them you want delivery before they start checking you out. Also, realize that the bagers work for tips. They will only deliver the groceries to the bottom elevator down by the lower small circle that goes out to the gate. So if you have a lot, you will want to have the bellhops take a cart with some bins down to help you get it back up to the room. Or you can carry it up in the grocery bags if it isn't too much to manage. Also be sure to tip the delivery guy if he does good job and doesn't bust your eggs or smash your bread, etc.