If you're going to Montreal have a look at Mont Tremblant. It's not far from Montreal and has some simply gorgeous scenery. Also, have a look at the Circuit Mont Tremblant website; there might be some racing at the track while you're around!
It's one of the best tracks in the world, too, imho.
As far as things to see, both Ottawa and Montreal have a lot of museums and historical landmarks in them, if that's what you're looking for. I don't know specifics as I haven't really been to them in either city (haven't been to either city all that much, either, actually) but I'm sure the municipalities' websites should have a wealth of information on them.
Are you visiting the Toronto area at all? As you've said the rest of the trip is planned, what stuff are you going to see here (assuming this is a stop on your schedule)?