Last season's Group I Vinery Stud Stakes winner had the option of the Group III JRA Cup or the Group II Stocks Stakes.
Corstens, who trains Montoya's Secret in partnership with his father Leon, will run her against her own sex over the shorter trip.
"They are both worth the same but the Stocks is a Group II for mares, plus I want to give her one more run at the mile before we step her up in
Montoya's Secret was beaten under four lengths when finishing eighth behind Hell Or Highwater last time out in the Listed Heatherlie Stakes over 1700m at Caulfield on September 2.
Corstens took the opportunity to take Montoya's Secret to gallop at Moonee Valley on Monday and was delighted he did.
"With that little bit of rain overnight she just loved the more forgiving surface there and she's come out of it really well," Corstens said.
"Her two runs back have been ok but not as good as we'd hoped. She just doesn't let down properly on a hard track and I'm putting the last start down to the track.
"I'm using the track as an excuse but I could be wrong, it might be that she just hasn't come up but we'll find out on Friday.''
With regular rider Noel Callow suspended, Corstens has been able to secure an able substitute.
"We've booked Joao Moreira to ride. We were able to get the Magic Man and thought why not use the best in the world?" Corstens said.
"Friday night is the fork in the road for the preparation and she needs to run well."
