They cut regional flights and focused on LGW, MAN and GLA. At one time they went to EXT (this was shared with STN for a few years), LBA and others.
STN had good links with Canada until more recent times. Through the 70s and 80s Wardair had regular service with DC10s and 747s, Worldways and others I can't remember came in as well.
Transat came in the 80s initially with dedicated flights and then shared from the late 90s to early 2000s.
Royal had up to 10/11 weekly flights to various destinations around 97/98 after being kicked out of LGW for poor timekeeping. They got back into LGW the following year but maintained 2/3 weekly flights at STN for a couple of years. So for a while there were two operators from STN to Toronto. I think Royal then merged with either Transat or Canada 3000, or went bust.
Thomas Cook flew to Vancouver for a summer around 2005 due to lack of slots at LGW. I'm pretty sure this operated over the school summer holidays either the year before or after.
Finally, there was Globespan and their daily service to Hamilton. Of the more recent links, this was the only one admittedly that wasn't a LGW outcast.
I'm sure I've missed some others, but although it should be noted the market to Canada has changed over time, flights from STN have always been popular when they have operated. I agree LGW has the larger traditional connection, but STN's place in the history of links should not be discounted.