It's 5.7 km. And a straight line on Highway 7. Which flows a lot better than most Toronto roads - even in rush hour! And that's the current plan ... I'd think that there'd be future Woolwich growth still be towards Guelph - which will close the difference to 3 km. Heck, I wouldn't be surprised if Woolwich tries to expedite growth there, rather than the big expansions the province is imposing on Elmira and St. Jacobs (which raises another interesting passenger corridor question - perhaps the streetcar in Waterloo needs a branch).
Years ago there were lots of people commuting between Guelph and Kitchener/Waterloo. The only thing that's changing is the driving is getting shorter and shorter. I don't see how Guelph would be a bedroom community to Toronto, but not to Kitchener!