Reconnecting the two halves of St Clair (which AFAIK were never actually connected by a formal road) isn't going to happen, given the presence of the ravine & trails, residential areas and the railway. If you really want to travel from one St Clair dead end to another, it's not a huge inconvenience to use Moore, Southvale, Millwood/Donlands and O'Connor; other than that, the two halves function as entirely separate streets.
Someone mentioned the Dupont/Dundas/Annette intersection. At the risk of sounding like a broken record, I think that needs to be regraded and made into a roundabout, or at least simplified with the removal of that stupid traffic island.