I'm suprised Montreal didn't just use the pool from the '76 olympics. It's old but it's pretty nice (of course it's been 10+ years since I swam in it).

The Olympic pool was probably part of the event facilities plan, but the number of actual events and disciplines is more than twice what it was for the '76 Olympics- add in women's water polo and synchro, a bigger men's water polo field, twice as many diving events, and and a significant number of new swim events (50s, men's 800, women's 1500, women's 4x200 FR) so you need about twice the pool space for this event that you had for those Olympics.

The 76 Olympic pool is indeed a sweet venue. I loved swimming there when visiting my parents !