I buy and sell things occasionally on Marketplace and Kijiji. If it is not a cash porch pickup, I use bank etransfer which has become the most common way to do small purchases in Canada.
BTW don't get me started about US postal money orders, a few years I got one for around $600 as a payment for my services to a customer in US. My Canadian banks would not cash it, so on my next trip to the US I tried to cash it at a post office in the north Detroit suburbs. I had to visit at least eight locations before I found a teller with enough cash in their drawer to cash it. Just sayin..........lesson learned.