My son and I did Beaverhouse to Poohbah via Jean and returned the same way in late-June a couple years back.  Took 2.5 days to get there and 2.5 days to get back.  Could be done in 2 days each way with favorable or no wind.  

I could imagine the Maligne being very fast in May.  Even late June we had one very difficult swift where we almost didn;t make it upstream.  After 2 tries, qwe made it.  Our fallback was to float down to the LLC village and pay for a drive up to Beaverhouse.  

We also fought a westerly gale all the way across Quetico Lake and almost didn't make it through Beaverhouse back to the car.

Great memories though...and the 3 days of fishing on Poohbah were simply amazing...big fish all over.

Another option is get an RABC, BWCA and Quetico entry permits and paddle from EP14 or 16 to the LLC ranger station....I've toyed with this, but have yet to actually do it.