There are a few dive shop options available within Ottawa for open water training that I am aware of.
PADI Shops include:
Kanata Diving Supply:
Kanata Diving Supply
Diver's Wearhouse:
Diver's Wearhouse - Home
Sharky's Scuba:
Ottawa Scuba Diving - Sharky's Scuba
There is one NAUI shop, Burton's:
Burton's Dive Service & Gear - Ottawa, ON Canada
I would suggest visiting the shops to see what the instructors and shops are like. As a new diver my experience is decidedly limited to only a couple of the shops on this list.
If you haven't already done so, there are a few threads on this board about questions you should ask a potential instructor or local dive shop (LDS) when considering training with them.
I did have great experiences with my instructors for the certs I have completed, and think that the combination of instructor and shop you choose to do business with is important when starting out.
Just my $0.02.