I think it will depend on the kind of winter they have up there?
Been down the Maligne 2 x, never paddled up.
Both times in Mid-May. 1 x the water level was "low" by normal snow melt levels,
 
The other time the current was really moving.
The portages were all flooded out.
In spots you could see "whirl pools" and if you got into one, you could feel the power of that current.
I remember thinking I was glad I wasn't coming upstream. :-/

I'm sure it's been done in high water conditions with the right people, but I would definitively have a plan B. :thumbup