Mystery bird - help!

This pretty grey bird was warming itself in the sun at the McKenzie Marsh in Aurora. I've looked and looked but cannot identify it. I've never seen one before so I'm wondering if it's a stray from afar. It looks like a flycatcher but none of what I found on the Internet quite matches it. It looks somewhat like a vireo, but the size is wrong. It's about the size of a waxwing, maybe a bit smaller. Anyone who can help, I'm all ears. Thank you!

Update: With help from John Van de Graaff and also from the Ontario Field Ornithologists (who also posted my photo of the bird in their Rare Birds Gallery for November which is very nice of them), the bird is undoubtably a Northern Mockingbird. With some further research on the Internet it shows that their territory reaches this far north in the summer but he should be flying south for the winter and that's where he was headed when he took off, flying south...safe journey!