With certainty, if PCL still offering the same Cruise Fare Code (3 alphanumerc) today that you booked under, then a re-fare is possible.
If the current Fare Code has expired and the new price is therefore a new Fare Code, it seems some agents can finagle a re-fare, but I would expect a cancel/re-book.
Also, it is possible to "lift and shift" some things to the new booking and not have a "do over".
In the situation of a cancel, try and plan to have the time to go in and cancel reservations like excursions and such that you are going to lose anyway. When self-cancelled, this should trigger a refund back to form of payment. IOW, "clean up" your res file before the agent executes the cancel/re-book. Advice for all, but tagging @MsSoCalCruiser.
Be aware in advance if you can re-book your air at similar cost or not. If not, have that discussion as to whether they can preserve the air. Have TA speak to someone at PCL because this can happen. Understand that you still have good acceptable flights to book and will any airfare increase cancel out out the cruise fare savings you are going after.