Not sure about other provinces but I think the subsidies in Ontario are up until 2020. If the paragraph I list below from the Economist is true, I can see why its by 2020.
The falling cost of batteries will make the cost of owning and running an EV the same as that of a traditionally powered car in Europe by the early 2020s, even without the hefty government subsidies that many rich countries use to sweeten the deal. Better batteries should also conquer “range anxiety”—most pure EVs now run out of juice after around 100 miles (161km). If battery costs continue to tumble and performance improves at the current rate, the price of a car with a range of 300 miles could hit $30,000 by the early 2020s, according to Exane BNP Paribas. Slicker technology will also mean charging in minutes, not hours.