Another old bridge which I don't think has been mentioned is the original reversing falls suspension bridge in Saint John, built in 1853. It might have been the oldest suspension bridge in Canada:
http://new-brunswick.net/Saint_John/vintage.html
Today there are two spans in that location: a railway bridge from 1885 and another bridge built in the early 20th century.
Another interesting historical bridge anecdote is that the Macdonald Bridge in Halifax, the older of the two current harbour bridges, was actually the third bridge to cross the harbour. The first two were railway bridges built in the 19th century that were destroyed by hurricanes.