A: No, the Surprise you draw via Mystery Play* cannot be used to stop the previous Canceling of your play. It’s far too late. Whatever card you played has been Canceled, and that’s that. With no Surprise available, you could not stop the Surprise, so you have moved on and taken your next game action: choosing to use Mystery Play.

Since choosing to use Mystery Play will always disrupt the immediacy required for a reactive Surprise play, any Surprise drawn via Mystery Play would have to be used for it’s in-turn function.

Note that you may be seeing this FAQ because your deck has a version of this card with a different name. There are so many analogues for Mystery Play that you should simply check the Fluxx Comparison Chart. Highlight the row for the Rule: Mystery Play, and scroll across to the deck you have to find the card this question refers to.