A: Sometimes. Legit Steam/Uplay saves are encrypted with your specific user ID. You would need to hex-edit the save file or use a save converter tool. It is easier to download a crack-specific 100% save.
C:\Users\YourUsername\AppData\Roaming\Ubisoft\Assassin's Creed 3\Saves Assassin-s Creed 3 Save Game Location Crack
If you are playing the Remastered version released in 2019, the folder structure changed slightly to accommodate the updated engine. A: Sometimes
C:\Users\YourUsername\AppData\Roaming\uplay_emu\Player\Assassin's Creed 3 Remastered Assassin-s Creed 3 Save Game Location Crack
Do not confuse "cracked save game location" with "cracked .exe file." Putting a save file into the wrong crack's folder will result in the game saying "Save data corrupted."