As mentioned above, BUF is an airport many Torontonians use (OK BUF was sluggested). IIRC Megabus stops at the airport, though there may be other options.

X 4 tickets will save a lot of money.

Also, many if not most OTAs will let you set up a price alert when a fare drops, so I suggest signing up for their emails.

I fly to YYJ several times a year so I'm very familiar with the extra taxes involved with cross border flights

And yes, if you see a good fare, pounce, they often don't last.