When your museum is unveiling a major expansion plan with Frank Gehry at the controls, it is supposed to be an unabashedly celebratory occasion. But for the Art Gallery of Ontario, today’s news conference will be a decidedly mixed bag of architectural grandeur and political damage control. The Gehry design will doubtless wow the critics with “a spectacular multi-story tower extending the AGO into Grange Park on its south side and bringing the park visually into the gallery.” But questions about the AGO’s decision to completely scrap its last expansion plan, as well as charges that the gallery is unilaterally pulling out of a 1989 agreement that it would never again expand, are sure to overshadow the proceedings.