MEXICO CITY( Reuters)-Two years after workers at Mexico's Tridonex auto-parts plant began a campaign to replace a union that they accused of failing to push for higher wages, they will get a chance next week to elect a new group to represent them. Tridonex's unlisted U.S. parent Cardone faced U.S. government scrutiny last year in one of the first labor complaints under a new regional trade deal after workers said they were being denied the right to freely select their union. The vote, scheduled