I've been wondering about how they're doing this and it turns out it's not only extremely time consuming, but unbelievably expensive. 

"For shows based in Canada, where there is a two-week mandatory quarantine upon arrival, casts and crews will stay put as a trip to the U.S. will derail plans  to resume filming the week after Thanksgiving. (I hear some Vancouver-based series were given Canadian Thanksgiving off last month and will work through the U.S. holiday next week.)"

The Difficult And Expensive Reality Of Filming TV Series Amid The Pandemic