I had traveled past this particular bridge many times, and finally was able to spend some time exploring it. I was intrigued to find that the artist collective group known as "General Idea" had used the bridge as a site for an installation a few years back. If anyone has any further information regarding the history of this structure, feel free to share it.
The bridge was built on the Don River in 1933 to replace an older wooden bridge which had been damaged by ice in the early 1900's. The original cost was $70,864.07. It was closed off in 1964 after the construction of the Don Valley Parkway, whereby it was considered obsolete. It was disconnected from the road network, and fenced off to prevent pedestrians from accessing it and/or the CN Rail line. The City of Toronto considered demolishing the bridge, but found that it was more inexpensive to maintain it and still continues to inspect it to this day.