I've been twice while on business and absolutely LOVE the city of Montreal....
...just hate the tobacco taxes! :laugh:
As far as cigar smoking, the LCDH is on Rue Sherbrooke. Very nice staff, great selection of cigars, and an awesome lounge that will serve you up coffee, mojitos, scotch, whatever you choose to accompany your cigar. The weird thing about their lounge is that they won't let you smoke cigarettes or machine-made cigars (even if its a machine-made one you just bought from them) in the lounge.
Not too far from it is a bar called Stogie's on Rue Crescent. They have a humidor, but they're more focused on the bar aspect (and 90% of the crowd is there to smoke cigarettes, not cigars). Still, a nice lounge and worth checking out.
Those are about the only places I know of in Montreal you can smoke in. Like most of the rest of the world, smoking bans have taken hold, but at least you can still partake inside of cigar shops. Also, be prepared for the tobacco taxes, since Quebec Province's are the worst in Canada. Expect $30-40 for a churchill-sized cigar or $20-30 for a robusto or corona sized one.
Having gone on business both times, I didn't get a chance to see a ton of sites, but I did go to the Art Museum, which is also on Rue Sherbrooke, not far from the LCDH. During my first visit there in 2008, it ironically enough was showcasing Cuban Revolutionary art. :laugh:
And one restaurant that really stood out in my mind was a great steakhouse over by the waterfront on Place d'Youville called Gibby's. The building it's in looks like it was an old stone stable or barn, and all they have to announce themselves outside is a little wooden pub sign...so at first you look at it and think it's a bar (a la Cheers), but if you go inside, it's steak paradise!
Have a great time in Montreal!