The answer to this question is subjective, depending on the airports you are travelling from and to. A major airport in a big city is considerably cheaper in comparison to travelling from a smaller region of Nigeria to a small airport in Canada. The latter scenario will almost certainly mean internal flights and this will increase the cost of air travel. If we travel from the city of Lagos in Nigeria to the city of Toronto in Canada then the results are fairly cheap.
To travel immediately, with no notice you should expect to pay between £675 - £800 for a one-way flight and roughly £1,000 - £1,200 for a return flight, bringing you back to Lagos two weeks later. If you are booking in advance then the rates are cheaper still. For example, if you are set to travel in January 2012 then you would expect to pay £650 - £750 one way and £1,000 - £1,500 return. The flights are with Lufthansa Airways, which seems to be one of the largest providers of air travel in Nigeria.
All of these flights include layovers in Germany, France or the U.S. And you should expect to be travelling for up to 28 hours before reaching your destination, although some routes provide a service that will take you to your destination in only 17 hours. Flights into any other airport in Canada, including Vancouver, will increase the price and you should expect to pay at least £800 for a one-way ticket and almost £1,400 for a return ticket. Getting flights from smaller airports in Nigeria is difficult and you will have to rely on smaller planes to major airports for any international travel.