I am sure the provider will be happy to have you cancel 2 weeks out, giving her time to set up something else. (Not that she will be happy you are cancelling but happy to get as much advance notice as possible)
Many guys will cancel at the last minute, or just not show up, which of course is not very professonal or courteous.

If you feel like there is a high chance of you cancelling, I think you should cancel now. The more time you give the girl the better chance she has of filling your slot. Without having more info from you its hard to tell. You can certainly play it by ear for a few more days but be fair to the girl you booked and err on the side of you giving her a bit too much time (if there is such a thing) rather than too little time.

cancel

at the very minimum..24 hour notice..schedules change..people get sick..they need to rebook to recoup..

....gentlemsn, and offer a cancellation fee.  If you change your mind, and would like to visit with her in the future, she will remember your kind gesture.

Hugs and Kisses,
Kelly

The more advance notice you give her, the easier it will be for her to fill the now empty time.  Offering a cancellation fee would be nice, but IMHO, not really needed unless you were cancelling at the last minute, which you are not.  But, that's up to you.

Swim