Toronto has a larger subway system than Montreal, with much wider and air-conditioned trains. Toronto has a more light rail, more commuter rail, and more buses (including BRT), and transit higher ridership per capita and mode share to show for it. I can't find any evidence that Montreal's system is twice as large as Toronto's.
The STM has actually been in decline for years now because of budget cuts that resulted in 7.9% less bus service today compared to 2012.
STM bus ridership has declined by more than 13 per cent over 5 years
If you look back even further to 2006, you will find that bus ridership of STM actually has declined much more than 13%. In 2006, STM buses carried 374.8 million passengers but in 2017 they carried only 271.6 million, a whopping 27.5 percent decline. Seems like the Metro extension into Laval masked some massive ridership losses on the island. But even with the Laval extension, the overall ridership of STM still declined 1.9% from 2006 to 2017.
Compare that to TTC, where bus ridership increased by a whopping 32 percent during that same time frame, from 344.8 million passengers to 456.9 million annually, while overall ridership increased 18%.