Final Fantasy will require GBA
And ship with a GBA/GC link cable.
Final Fantasy Crystal Chronicles will require GBA consoles for its multiplayer mode, Nintendo's Japanese website seems to have confirmed. According to reports, the final release version will not support standard controllers as the E3 demo apparently did, but to lighten the financial blow there will be a GBA/GC link cable bundled with every copy of the game sold.
Meanwhile, single players will be able to choose whether they want to use the normal Cube pad, the GBA, or a mixture of the two for controlling the game. As with multiplayer, when the GBA is connected it acts as a menu screen and also offers a map function.
Although it's not absolutely definite that the European or American requirements for the game will be the same, it's difficult to imagine a different arrangement - particularly given Nintendo's baffling obsession with connectivity as witnessed at E3.