do I need a visa to transit Hong Kong travelling from Ottawa, Canada to Colombo, Sri Lanka?

It depends on your nationality? I assume you are a Canadian. Then no visa is needed for you can enjoy 90 days visa-free in hongkong.

And on the return, I am going through Shanghai. And yes, I am Canadian. I assume no visa necessary. Would I be allowed to go outside of the airport, either in Hong Kong or Shanghai? Sandra

Yes, you can go outside of the airport. But you need to apply for a 72/144h visa free transit or a temporary stay permit (transit less than 24h) before heading to Shanghai.

Can I apply for this at the airport or do I have to do this before I leave Canada? Thanks for your assistance.

Prsent your passport at Hongkong Airport and you will be allowed to get out. For return trip, you need to inform your airline about your layover in Shanghai before boarding, fill in the Arrival/Departure Card, and get a stay permit at the immigration counter at Shanghai Airport. Then you will be allowed to leave the airport for a trip!

Thank you. For all your answers. Last question. Is there a cost for the stay permit I will get in Shanghai?

No, it is free.