Sisteron is always a massive breakaway stage. Nothing will happen in the bunch.
Yes, plenty of possibilities for tight quircky slopes at smaller roads in the region.
Of which partly is the case for mid section of the stage. Unfortunately the ramp-in to Sisteron and the loop is too simple and miss complexity, hence sprint trains have the chance to catch up on the break.
Unless the break turns out to be really strong, consisting of riders from the sprint teams.
I wouldn't fully count on a sprint in Sisteron.
Especially taking into account of possible cancellation of Auron stage, and, hence, that every meter counts in the GC.
*Edit;
I'm devastated regarding the indeed very likely cancellation on saturday - been extatic since stage was revealed, having climed it two times myself, 1.st time with Cîme de la Bonette du Restefond (2802m.a.s.) as a "starter" (quite a portion, though), 2nd time in larger group from Nice with 90k ramp up at speed. Both times Auron climb felt far harder than the cold numbers tells.