Flying from Canada (I am a Canadian citizen) to Sri Lanka with a layover in Shanghai for 18 hrs

I'm afraid you cannot get 72 hours visa free, because it regulates that you can only make one stop in China and without a Chinese visa. So you need to apply for a Chinese visa in advance in Canada.

Ok, so I have been reading further and it is possible, I can get 72 hour and visit both Shanghai and Kunming but I would have to go back to Shanghai airport to leave the country as it seems to stipulate that you have to arrive and leave from the same city. It is starting to feel like a hassle, I may need to look into a visa, however, on my return flight to Canada it is the same thing in reverse, perhaps it is possible to visit one city on the way there and one city on the way back? Thanks for your reply.

Dear, first, you cannot get the 24 hours free visa because you cannot leave China within 24 hours(Shanghai for 18 hours and Kunming for 21 hours).

Second, you cannot get 72 or 144 hours free visa because you make two stops in China. And it regulates that the flights can only stop in one Chinese city, meaning passengers have to enter and exit from the same city. So on your back trip, you can get the interline tickets that allow you make one stop in China.

Yes, if you reread what I wrote, I have agreed with you on that point I also pointed out to you the reason (you need to arrive and leave from the same city). What I was asking was can I tour just one of the cities -spending time in the airport for the other- and then on the way back (since I once again am coming from another country and stopping in China on my way back to a third country) tour the other city.

On your first trip, if you fly Canada – Shanghai - Sri Lanka, you are eligible for the 72 and 144 hours free visas in the meantime.

On your back trip, if you fly Sri Lanka – Kunming –Canada, you are only eligible for the 72 hours free visas. If you fly Sri Lanka – Kunming – Shanghai – Canada, and your stay extend 24 hours in Kunming and Shanghai, you cannot enjoy any free visa and need to apply for a Chinese visa in advance.

The 144 and 72 hours visa free policies both regulate that you need not only enter and exit at the same city(only make one stop in China) but also you can only stay to move in the limited areas (144 hours for Shanghai, Zhejiang, Jiangsu; 72 hours for the city you enter) . 24 hours free visa allowed multi-layovers in China but you must leave China within 24 hours.