It depends. Kelly Rowland has a much larger international fanbase, however none of her recent music has really touched people locally or internationally. But people may purchase Kelly's music just because of her past hits. Also she is actively on tour so it may cause the public to become interested in her again. Her last album with the monster hit "Motivation" sold 245,000 to-date.
Let's get into Ciara. Ciara has a harder, up-hill trek. Ciara has gotten alot of negative press from the urban music community and i still dont know why. She does have the advantage of having a hit with "Body Party" and it seems she went from irrelevant to R&B front runner in 6 months. Ciara has a much more successful solo career and fans seem to be enchanted with Ciara Princess Harris all over again. Btw, to answer the big question,
Basic Instincts sold 116,000.
It could go either way, Ciara still have 5 weeks to get her face out there and it looks like that's exactly what she is doing. Kelly is currently on tour with The-Fail i mean, The-Dream and being on the road does increase your chances of sales.
Bottom line.
Going their current space i see Kelly doing, 65k-85k.
Ciara could beat her with a 75k- 100k.
Ciara is younger, getting more attention, and her music is actually connecting to the younger crowd. All the "Dirty Laundry" and semi-beyonce shots in the world wont change that.

"And that's the bottom line, cause Stone Cold said so."