Other 'unconventional' sources of oil exist in countries including the USA (oil shale), Venezuela, Trinidad and Tobago, Madagascar, and the Congo. These are not yet being commercially exploited, but are being commercially explored.
Tar sands are mixture of sand or clay and bitumen, a thick and heavy form of petroleum, sometimes referred to as 'heavy oil'.
Bitumen needs refining to bring it to the grade of synthetic crude oil. This involves large amounts of water, chemicals and natural gas, which requires additional infrastructure.
As you can see exploiting the tar sands of Canada, and other 'unconventional' sources of oil, comes at a very heavy price.