I've sat everywhere in Montreal.
The main Grandstand across the pits is good for only the grid formation and start (hopefully not a Safety Car start!)...and not much else.
The hospitality is good for comfort and food and lots of TV screens but nothing else.
[I've been offered both Main/Pits Grandstand seats and Hospitality last year and this year, but I declined in favour of Senna Hairpin.]
The main Hairpin wasn't a favourite, to be honest.
In recent years i've always found myself seated at that Senna Hairpin which overlooks the start line area (HAM/BUT tangle), the first corner breaking (Hamilton punting Webber and always fun), the pit exit lane (Maldonado binning it) and the exit up into the back (last year SCH v KUB on the grass; this year Heidfeld crash).
Plus you can always leave your seat and go right down to just behind the Marshals post and see the cars circulating at close quarters behind the photographers.
If I were you, I'd walk around the Island during practice and get a feel for the ground shaking - if you get close enough - on either side of the big Casino where the cars are fastest.
DRS in Canada was in the very fast bit into Pit Entry and then on the Pit Straight...a Double DRS.
It's always special when you go the first time. There's nothing like the first time. Plus Montreal is a HUGE, HUGE party. The downtown is a 10-12 min Metro/subway ride.
In contrast, I remember going to Hockenheim the year JV won the WDC and it was like over a one-and-a-quarter hour limo ride from Frankfurt. I was wondering: "
Where's The Party?!?" 
EDIT:
Looking forward to heading down to Austin...should be a big party!
