: Actually you are close, I believe the longest portage; grand portage, is
: closer to 8.5 miles, not bad for crossing 6000 miles by rivers and lakes.
: Gary and Joanie McGuffin made this trip and wrote a great book about it.

Strike 2 :-)

The Methye portage between the Churchill River and the Clearwater River is 19 km long (about 12 miles). It is on the standard fur traders route to get up to the Northwest (Lake Athabasca), and then on to the West, going along the Peace River. I would be surprised if there wasn't a longer one somewhere.

In 1999, Ilya Klvana paddled a kayak across Canada. His longest portage was 35 km. but this may not have been a typical route for fur traders. Take a look at the included link. The second link is the one with the Methye portage. I have been thinking about doing this one for a long time... just have to convince some other crazy friends to join me!