With Canada's three main political parties all getting around 30 percent support in polls, the odds of a period of political instability after the Oct. 19 election are rising.

It could also shed an awkward spotlight on the constitutional role played by Governor General David Johnston, who is Queen Elizabeth II's representative in this member of the British Commonwealth.

A proposal from Canada's Green Party leader Elizabeth May for the two main parties on the left to take power immediately if Conservative Prime Minister Stephen Harper fails to get a majority — even if his party has more seats than anyone else — has triggered concerns that Johnston will face a very difficult decision.