Why was it flying over Toronto? Canada was a stakeholder in the project, the Canadarm was designed and built in Toronto by SPAR Aerospace. The overflight was part of a trip by the Enterprise to the Paris Air Show. NASA decided this was good PR.
The Enterprise never flew in space, it was used to practice landings on earth and verify the flight worthiness of the design, and it was retired in 1985.
Over the years I have had a great interest in space flight, manned and unmanned, the shuttle was an amazing achievement in many ways, and a total disaster in others. I'm sure you've heard the comment that a camel is a horse designed by a committee, well the space shuttle was obviously designed by a committee. A perfect example of how a government institution (NASA) compromises to achieve a mission that might have been done much, much cheaper, and safer. I'm not going to detail what was wrong with the design, suffice to say that two astronaut crews were killed directly because of known flaws in the design. A quick Google search will give you much more expert opinion.
The fiscal crisis in the United States, has spawned a for profit private sector space industry. It's about time.
ReasonTV has their own take on the past, the recent final flyover, and the future of manned space flight.