Someone once asked why there were so many British actors on TV and the answer given was they were less expensive.
IF that is true, that might also answer the question of why a lot of locations were in Canada.
I don't know the answer, but Stranger Things was just ONE of the well written series we've binged on.
The very first binge we ever did was LONGMIRE and that hooked us.
Canada’s industry is unionized, but even so, apparently, it is much cheaper to film here. I guess the Hollywood movie workers have priced themselves out of many jobs. Yes, Canadian actors as well probably come much cheaper. Breaking into the US is a dream for them.