Sorry but there are never deals from DCA (only AC) and IAD (only UA) to YYZ. No budget carriers do these routes. Same with BWI. The only way I do it for (a lot) less money is WN from BWI to BUF and then drive. Car rentals in BUF are reasonable and Megabus goes from BUF to Toronto as well (but check the schedule). The current fare I have on WN is $49 each way with a bit of a tax on top. AC would be five times that. It's a two hour drive. I drive from Toronto to BUF and do a car rental at BWI. Southwest.com has excellent car rental deals. The DC airports are tied up with international dealing and budget carriers don't fly to Canada and Westjet hasn't had much success on US business routes.