Where can i get the cheapest return flight from toronto to manchester?

I want to travel to manchester from toronto on around 29 april and planning to return on on around 25 may. But my dates are flexible upto 5 days up and down. Can you please suggest me where should i look for the best deal. any website or anything. thanking you in anticipation.Where can i get the cheapest return flight from toronto to manchester?
The lowest current published fare on that route for your travel period is $463 plus taxes and fees if you stay under 1 month, and $567 if you stay over one month.

That price is published by United, however US Airways offers it as a code share flight for $618, and Air Canada and Continental for $662.

The fare was a little lower for any return trips completed prior to April 30, but just went up.

All prices are in USD and subject to taxes and fees.