The options to Hamilton and Toronto direct are:
Thomas Cook, which operate some services on behalf of Transat
Transat from LGW, and occasionally - once a week, LHR
Globespan from LGW to Hamilton (they offer a coach service from Hamilton to downtown Toronto if required)
Believe Skyservice will be taking up some of the Zoom slack
In terms of the "majors" BA and Air Canada. On the return, Air Canada offer the daytripper which departs at c. 0900 and arrives Heathrow same night, c. 21.00-ish - no jet lag, but a whole day wasted in the air if you want to look at it that way.
Plenty options via CDG, Schiphol and Frankfurt with AF, KLM and AC/LH.
Pricing around Xmas will inevitably spike, so best to think about buying now to get the cheap prices, on a credit card so the "protection" kicks in...