When the Portland Baroque Orchestra’s artistic director of nearly three decades announced her retirement, the organization began a years-long search for a new leader. Starting this weekend, the three finalists for the job will perform in front of live audiences in a series of concerts to determine who will lead the early music orchestra going forward. Interim Executive Director Dave Pearson and interim Artistic Director John Butt explain why taking the audiences’ opinions into account is an important part of the selection, and what these three finalists will bring to the Portland institution.