I have a copy of Pokemon Firered on my Gba and I want to trade pokemon between it and my copy of LeafGreen on my wii using MGBA using a Gamecube to Gba Link cable. Will it work.
No, unfortunately the link cable between two GBAs and the link cable between the GBA and the GameCube work completely differently and are thus not compatible.
mGBA Forums > mGBA > General > Trading Pokemon From Wii To Gba Using Gamecube To Gba Link Cable.