Here's a rough idea I have:
For the north-south route, build a new bus-only road at the Wellington curve that joins up with Colborne street via a new bridge. This would eliminate the need to expropriate buildings on most of the existing 4-lane stretch of Wellington and wouldn't interfere with the heavy traffic use the road gets to downtown.
-Keeps 2 car lanes on the existing Wellington CN underpass, but would likely require building a new underpass at Colborne, possibly for both cars and buses.
For the east-west route, use King and Queen from Colborne to the Thames, and build a new bridge connecting Riverside and King. This keeps Dundas free for closures for festivals and whatnot.
-King and Queen would still be one way roads, 1 lane with parallel parking during off peak times, 2 lanes with no parking during peak times.
-Use Dundas east of Colborne. This stretch is wide enough to accommodate this, but parallel parking through Old East Village would need to be eliminated. Sacrificing a lane on King east of Colborne for parallel parking wouldn't impact traffic much, Queen was already reduced to 1 lane from Quebec to Adelaide for more parking and it works fine.