What the others said. Even converting between regions on the same system can often be a massively involved affair. Two similar power consoles is not necessarily the worst thing (people sometimes want console to handheld) but I would still expect to be doing a lot of work -- most times save data does not need to be changed between ports (still going to have the same general gameplay and features, not like the 8-16 bit era where one system might have the devs fork out for save memory where another will not and the games also tended to be rather different).
What we normally suggest people do is find/make some cheats (
https://web.archive.org/web/20080309104350/http://etk.scener.org/?op=tutorial is for the GBA but works much the same for any device*) and you can then use those to replicate your progress or just be infinite health/ammo/whatever such that you can get back to where you were without too much trauma.
*theoretically you only have to do the NGC if that is your destination, however I would do the PS2 as well as it could make life easier to maybe copy data across/remake it in RAM (rather than say finding all the stats in an RPG you might find one easy to change one and then have all the others right next to it, and can then do the same on the other system rather than having to find a cheat for all stats).
But otherwise you will need to figure out what wrapper formats, if any, the systems in question use and thus how to disregard them. You then get to do something useful and figure out how the data is formatted in each save format (what data is stored and where) and here what differences there might be and how to sort them (at a minimum it might be different lengths for sections, plenty more advanced things that could make life difficult too), and then how you are going to set about sorting any hashes (for a one off I might well hack the game to disregard the save hash when loading, load that modded save in an emulator and then the game itself will tend to rather nicely fix the hash for me such that an unmodded game will then consider it good. Though if the systems use wrapper formats, the wii has something like this but many older things did not, then they might also have hashes to worry about).