The existing tunnel is south of Randolph, it's about halfway between Randolph and Bloor. That tunnel is lined up nicely to connect to Dundas West Station. However, it's currently accessed from the platforms, and the eastern-most platform is accessed directly from the railpath. Once they add the extra track between the railpath and the eastern-most platform, they'll need a tunnel from the railpath to the access the platforms. They've been saying that new tunnel will be built at Randolph, I assume because there's extra space there to build an entrance, including an elevator, and still fit the railpath around it.
The question I don't know the answer to is whether that tunnel will then jog south and connect to the existing tunnel, or whether it will be an entirely separate tunnel only connecting the railpath to the platforms. This would force customers accessing Dundas West station from the railpath to go under, come back up to a platform, and then go under again. This would also mean constructing at least one extra elevator, so I'd think that if it's physically possible they'd connect the Randolph tunnel entrance to the existing tunnel.