Samantha Stosur is in the position of the big favourite but I have to disagree with that as first of all she didn't played at least one game here at Indian Wells, so she didn't proved to be in a great form as she was for example in other tournaments like Los Angeles, Osaka, French Open or others from last year.
About Julie Coin I have to mentionate that she is able to compete against difficult players as she has proved that even recently against Lucie Safarova, so I'm sure that she can be competitive against Stosur's level.
Samantha, is the player who depend a lot of his serve as this is her most strong point of the game, but without serve and also forehand she can be very easy in trouble as in those rallys from the baseline Coin should even dominate the play. From the defence point of view Coin can create trouble to Stosur and there not about only Coin, it is about Samantha's qualities and style of playing as she is not the player with stability from the baseline.
All in all, Stosur can play amazing tennis but that when she is in a great form, her attacking style needs accuracy, otherwise she can be very simple in troubles. Good Luck!