I am happy to report it seems to definitely be the real deal.
This particular flavour is available at Greg's Ice Cream, located on the southwest corner of the Bloor/Spadina intersection here in Taranna.
Now, I didn't do the ultimate comparison, which would be to start a small campfire on the sidewalk outside, go inside and buy a cone, then come out and toast a marshmallow over the fire before consuming first the marshmallow and then the cone.
However, I definitely noticed the roasted marshmallow flavour in the ice cream, which also had terrific texture. The one thing that had me wondering was the absence of telltale flecks of black from overly toasted marshmallows.
But even the colour of the ice cream matched that of a perfectly done marshmallow. Perhaps proprietor Greg Mahon is a perfectionist and tosses the overdone marshmallows.
Anyway, if you've had one of these cones, let me know what you think.