Martin also sent me this graph of the flow for 2009 at the outflow from Bigstone Lake:
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An interesting note was that the water metering station is now a "real-time" station and no longer requires manual reads. The station is expected to soon be added to the list of stations that are available to the public online!
So, if you want to run the Montreal River but missed you chance in the spring, now is the time. The Montreal River has lots of Class 1+ rapids and at the levels we paddled it was not at all technical (I ate a can of salmon while negotiating a series of rapids), but it was a lot of fun, especially the last third which had a couple of stretches of C1/C1+ water that were 3-4km long.
For information on running the Montreal, see Laurel Archer's book Northern Saskatchewan Canoe Trips. I also found a brief description and map online at http://www.princealberttourism.com/index.php?option=com_docman&task=doc_details&gid=129&Itemid=86 (down at the bottom click "download" or "view" to see some information on running the Montreal as a day-trip).
Follow Up: I posted some pictures as their own post. You can find them at http://pawistik.blogspot.com/2009/11/montreal-river-follow-up.html.