I think Halep will beat Sharapova. Assuming she's not overcome by nerves, It will depend on her ability to neutralize Shazza's blistering forehands hit right at her. If she can get them back deep, she will take control of the points and use her angles and ability to take the ball early to get the ball away from Sharapova's hitting zone. If she hits the ball short, Sharapova will win.
I know all about Sharapova winning 19 consecutive clay matches that extended to three sets, but Halep can win if it goes three sets. She is 8-1 this year in three-set matches. Yes, the one loss was to Sharapova, but Halep is a great three-set player in her own right.