No train, but there might be a bus. You should post on the Ottawa forum which might get a quicker response.
This question has been asked on Trip Advisor previously, although in reverse (Tremblant to Ottawa) at:
Not sure if there's a particular reason you don't want to drive, but you're about 2 hours by car from Ottawa. My wife and I drive to Tremblant from Toronto, and we come through Ottawa, use the Cumberland ferry to cross the river, and from there it's 90 minutes of gorgeous scenery to the Tremblant area...Edited: 08 February 2012, 23:03
You have to travel to Montreal and catch another bus to St-Jovite there. The alternative is going to Grand Remous then to St-Jovite. Neither options are very practical.
You should check on Craigslist or Kijiji for carpool ads.
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