I can tell you a little about Hamilton's Around the Bay Race. I have run it! It was first run was on Christmas Day in 1894, three years before the first Boston Marathon was run. Gord Dickson, one of Canada's great runners from the past won the race seven times in the 50s and 60s.
The draw bridge has been up on two occassions. The first was in 1961 to let a sail boat pass through. No runners got over the bridge before it rose. We were stopped for about 4 minutes according to my running log.
The bridge was also up during the race in 1996. I understand that about 40 runners got across before the bridge rose.
I greatly enjoyed my one race Around Hamilton Bay. I hope to go back and jog or just watch that race some day.