How to support legacy url alias' and/or support multiple url alias' (Conditional Pathauto?)
I believe the new-for-Drupal-7 Redirect module will provide what you need. Have not used it myself yet, but I used Path Redirect (which provides similar functionality for Drupal 6) to solve a similar problem. I generated a two-column table of values (old URL in one column, new URL in the other), and fed that to Path Redirect -- problem solved. Hope this helps.