To beat every team in the World Cup, line up at the goal and have your teammate pass the ball to you. Do a Superkick (A+B) and you should score. Build up a ginormous lead and then begin kicking the ball out of bounds until the clock runs down.

Select the two player versus mode on whatever surface you prefer, then play the game as normal. Don't worry about the results; this will work regardless of who wins or by how much.
When the game ends, instead of resetting the game, select tournament mode against the computer. Choose any team and select any options that you want.
At the start of the game you'll be playing on the field that you were playing on earlier instead of the normal Tournament field.