The 401 gets up to about 18 lanes in the city. If the area is so rural, what's stopping it from getting wider? Also, you may have picked up re the UNESCO reference that it's not just about finding a literal gap in the escarpment.
There's one thing about a massive freeway through an urban area, quite another through rural areas. When an intercity freeway gets so busy that it needs to be built to a massive urban standard, it's time for a second highway. And like I said, widening the 401 does nothing for Georgetown and northern Brampton, not to mention vacationers from western ON wanting to go to cottage country. The urban GTA should have a bypass. Also, A nation should have sovereignty over the UN. I know that concept doesn't have much currency on this forum, but that's a fact