I was recently in Ontario for my brother's wedding reception, during which I was able to fit some birding in.
The first place I visited was Lemoine Point Conservation Area in Kingston. Within about 200 meters of the parking lot, I had Mourning warbler, American redstart, and Canada/Magnolia warbler (all lifers). Other highlights included a Baltimore oriole (another lifer), some Common terns, and a family of House wrens.
In Ottawa, I went on a group excursion with a birding guide named Jon Ruddy. We spent the morning at Britannia Conservation Area, which is the top birding spot in the city. Warblers were everywhere, and we enjoyed distant but good views of Great and Lesser Black-backed gulls. Nine of the species seen or heard that morning were lifers for me.