Well, first off the hull is “hogged” as in “hog backed”. Having a hull that is hogged is not desirable, but sometimes a moderate degree of hog back does not impair paddling function as badly as one might expect.
Second, you have erosion through the green vinyl outer layer and through the outer ABS solid stratum of the Royalex into the “foam core” at both stems.
The “repair job”, which is truly grotesque, looks as if it consisted of someone slapping a rectangular patch of fabric, probably fiberglass, onto the interior and exterior of the hull with God knows what type of resin.
G Flex epoxy, made by West Systems, is formulated to provide better bonding strength to plastics, including ABS. More traditional types of epoxy have been used to repair Royalex boats with variable results, but these do not provide as strong a bond as G Flex does. I have seen repairs to Royalex boats done with conventional epoxy where a patch looked reasonably good sometimes for years, and then the whole thing flaked off one day down the road.
Amateur hack repair jobs almost always make a proper repair at least twice as difficult as it otherwise would be. The good news here might be that the repair job is so crappy and the bond so weak that the applied resin and fabric might come off easier than one might expect. If I am interpreting the photo of the interior correctly, it looks as if some of the fabric on one side of the patch has already come loose and chipped off. I would try getting under that edge with a paint scraper or putty knife and see if you can chip off the remainder of the fabric and resin. Anything that does not easily come off could be sanded off given time and patience.
That will likely leave you with areas on the inside and outside either completely or partially denuded of the green vinyl layer. These areas could later be covered with fiberglass patches properly applied. If you go this route, I would use some wooden spacer sticks to “jack out” the hogged hull section before applying the patches, This can be done by clamping a 2x4 to the gunwales transversely just forward and aft of the area you need to patch. Then cut some sticks of just the right length to act as vertical risers to jam between the 2x4s and the hull bottom to apply outward pressure and maintain it while the epoxy cures.
The damaged stems can be repaired by filling in and covering all of the areas of exposed foam core with G Flex epoxy thickened a bit with colloidal silica powder. Then after covering the core and “replacing” the lost outer solid stratum of ABS, sand the cured epoxy flush and fair and cover the area of damage with a longitudinal fiberglass patch.
Dealing with the hogged hull is trickier. Most Old Town Pack canoes are paddled sitting of a fairly low seat. If this is your plan, and you do not need room beneath the seat for your feet to be able to paddle sitting, you may be able to fashion some blocks of minicell foam to place between the bottom of the seat frame and the hull bottom to help push it back out into shape. Or you might place a thwart just behind the seat with a foam block between the bottom of the thwart and the hull bottom.
There have been quite a few threads on this forum detailing repair of Royalex boats, Here is one you might choose to review:
Here is a public album detailing the repair of a Royalex canoe that had been pinned and had sustained significant damage requiring interior and exterior patches. If you go through the photos individually, you will find a caption describing what is being done: