I never heard the Mosport-Mclaren link but I'm pretty sure about Mt.
Tremblant (I think I read it on their website when they had one). Maybe
it's like golf courses today, where you've got a big name designer (like
Tiger) and under him is a no-name designer who does the real work. The
Canadian racing scene would have been pretty tight nit then (it's not huge
now), so I'd be very surprised if there weren't a lot of common people
involved.
As to the tracks looking/feeling similar, there's a simple reason for that,
All the flatter land had been cleared for farming, so the only places they
could develop for race tracks was the stuff that was too hilly or too swampy
for farming ;)