If later in the season or in dry conditions I can attest to the possibility of a two hour mud slog...we did it in 2006...met db on the portage there :).  That was in August, beaver dams were 5-6 feet high at the time and also in low water conditions.  If your gang doesn't mind cavorting in hip deep mud then it just boils down to how fast you can travel in those conditions dragging the canoe in a few inches of water.   ;)