But, what if SCOTUS ruled that provision of the NJ law to be unconstitutional? The 17th amendment has no provision for a governor cancelling an election for a US Senate seat but does require senators to be elected by the citizens of the state. The governor can only appoint a senator if a US Senate seat is vacant not if a senate candiditate withdraws before the election. If Torricelli resigns, I can think any appointed successor would ouly serve the remainder of the current term.
Why are you talking about cancelling the election? It is not cancelled and there is no valid scenario in which it would be.