joinsをarrayで複数定義すればOK。
'joins' => array(
array(
'type' => 'LEFT',
'table' => 'gp_lists',
'alias' => 'GpList',
'conditions' => array(
'GpList.id = CpContent.gp_list_id',
)
),
array(
'type' => 'LEFT',
'table' => 'cp_lists',
'alias' => 'CpList',
'conditions' => array(
'CpList.gp_list_id = CpContent.gp_list_id',
)
),
),