Cheap Canadian flights to London?

So I’m planning on spending my New Year’s this year in merry old London, and I was wondering if anyone could recommend some good sites to get cheap airfare – either from Toronto or Hamilton to London (or Manchester if need be) – and I am hoping to spend $500 or less (Hey I’ve seen some summer flights for $50 + taxes so it may be doable!) because that’s about how much I have saved to spend LOL

Last time I went to England, I went to Manchester return for about $650 🙂