https://www.evisa.gov.tr/en/

This web-site allows you to buy a visa before you get to Turkey.

This will save time queueing at the airport, and the hassle of changing money before you arrive, to get cash in Euros or US Dollars if those currencies are not yours.

At the airports it is sad to often see tourists spending a long time waiting to get to the passport control, only to be sent back to join the visa purchase queue. Then they have to rejoin the passport control line at the back

I wonder how much the e-visa costs?  At the airport it is 45 US dollars and if you get it via the Turkish consulate in Canada it is about 125 dollars.  So it comes out cheaper to get the visa at the airport, you just have to make sure you go for the visa before going through customs.