Freezing is the choice for preserving left-overs, not canning, for several reasons.

First because the the additional processing would often render the food into mush. Foods containing meats require 75-90 of processing time in the pressure canner. A food that has already been fully cooked won't usually hold up that long under pressure.

Second because you have no way of knowing the pH or the density so the processing time required would just be a guess at best.

But if you chose to do it anyway and take the risks then yes it would have to be pressure canned - the gravy too - as both are low acid foods and both contain fats. Only high acid foods may be canned using boiling water bath canning. Sorry. Freeze the leftovers for safety sake and better quality.

Dave