To start a Career with any team, go to "Main Menu" > "Team Management" > "Edit Player". Choose your desired team and edit their players up to a rating of 78. The team should now be available in Career mode.
Select a practice or friendly match. Before the practice match, select the number of players for each team and set the camera to Pro. Start the practice match, then enter into the "Practice Arena" menu and go to "Select Sides". Have the other player go to your team or the opposing team. For the friendly match, start with one player. Set the camera to Pro in the pause menu in "Settings". Then, go to "Select Sides" and have the other player switch to the team he or she wants to be on.