I have only visited Columbus once and it was for the Romantic Times book festival so I did not see much of the city. What I did see reminded me of a cross between Klienburg and Aurora. It is about a month ahead of us in weather, meaning when I visited in May of 2010, their flowers had already bloomed and the weather was beautiful.
If I had more time there I would have liked to visit the COSI Columbus which is a hands on science museum and planetarium. However, there are various other sights to see including but not limited to the Columbus Museum of Art, German Village and the Scioto Greenway.
As Columbus is only a seven hour drive from Toronto, make it a stop on your way down south.