If you want a cheap flight from Edinburgh to Toronto, you've got zero airlines to choose from.
Toronto City Centre Airport is just one of the airports in Toronto. If you're not set on a specific airport, try changing your search from Toronto City Centre Airport to Toronto to see a broader range of flights – they might be cheaper.
If you're planning on going to Toronto during this time, you could take a look at other airport options. Or you could try to get a last-minute bargain.