Rectilinear halls work acoustically all the time. Ask anyone of this in Detroit, or Omaha, or Minneapolis, or Edmonton, and they'll tell you the rectangle is a surefire acoustic. So Montreal will join the long list of cities with shoebox halls....
Having said all that, I can't help but add that this interior design is a tad boring. I am tiring somewhat of all the blonde wood I am seeing just everywhere, of late, and this place is absolutely lined in it. Oh, well, it isn't my hall and I really don't care that much. I wish them luck getting it done and I'm glad they are funding it sensibly in these times. Basically "nice" exterior work from Diamond.