Those "souces" claim the show will film at new sound stages, and I find it a little odd that all the Trek shows are filming in different locations because they're all going to want to reuse the same standing ship sets at some point or another.
It wouldn't be Star Trek otherwise.
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Missausga is literally right beside Toronto, its part of the Greater Toronto Area, its probably like a 20 minute drive between the two Studios depending on traffic, so they can easily move sets, props, actors, and anything else they want to between the two sets no problem, so its not an issue. Most the Discoveries stuff goes into storage between seasons anyways, they don't just leave it permanantly at Pinewood Studios.
And they build the CBS studio as part of their huge investiment in Toronto, the GTA is becoming a huge movie/tv city, with a booming film industry. Also CBS is not Pinewoods only customer, although Bell Media which is so invested in Star Trek it bought Pinewood to expand it for more Star Trek .
And Kurtzmen already said they want shoot all Star Trek in Toronto from now, Picard was exempt because Patrick wanted it that way, plus $20,000,000 tax incentive from California likely didn't hurt.
Even the Children of Mars, the Picard prequel from Short Treks was shot in Toronto at the University of Toronto.
ST: Pike and ST: Starfleet Academy (the two new shows Kurtzman was most likely talking about), will also likely be shot in the Greater Toronto Area.
Its interesting how Star Trek Discovery has spawned so many spin offs already, Short Treks, ST: Section 31, ST: Pike, and maybe even ST: Star Fleet Command. Its been a huge boon for the GTA's economy.