If flying, consider buying a 3 day bus pass at the airport. was $18 when I was there. That will get you on the bus in from the airport, a $10 fare last time I was there, and on the rest of the STM metro and buses as well for three days. Cheaper than the locals on their stm pass card get around on.
Not sure if it gets you back to the airport as well anymore , but in my times there $10 in coins on Rene Leveque at the 747 route stops and that airport bus route will take you back to the airport.
If you drive there and don't want to deal with parking in the city, there is long term city surface parking lots out at south end of the yellow metro line, a few blocks walk from the Metro where parking was like $30 for about 30 hours or something like that.
If it is a nice day weather wise just walk downtown part of Ste Catherine. Green line McGill to Peel metro area.
Lots of shops, or entries into adjacent malls.
Yes lots of good smoked meat spots on Ste C. One is downstairs in a formica fittings time capsule that serves a great meal
If it is crappy weather the underground walkway system is very extensive too.
I would sit in meetings all day, then get the bus back to the core and go walking underground for more than an hour in a big loop before finding a place to eat dinner.
Or not a loop and catch the metro back to near my hotel.
Look up the Barbie museum. It is in a high end mall just a bit north of Ste C. It is a really interesting free activity even if you are not into Barbie dolls.
See if there is a festival running at Place des artes.
There is one most weekends from my experiences there.
A fun space to people watch if weather is nice too.
As to St-Viateur bagels, we took the Parc bus route out to get there from near the McGill metro station.
If you like your female strip clubs where you can sit 10' from the dancer on stage, I would recommend Club Downtown. Ste C near Drummond. Peel green line metro
Nice pubs just off Ste C too.
Nice smaller scale neighborhood main street to walk down with not too expensive cafes along the way if you pop up on the Metro green line at Verdun.