I am flying from Siem Reap (Siem Reap Air) to Phnom Penh, from Phnom Penh to Hong Kong (Dragon Air), from Hong Kong to Vancouver (Cathay), and from Vancouver to Edmonton (Air Canada).

My question is, when I get my boarding ticket in Siem Reap will I also get the ones for Dragon, Cathay and Air Canada or do I have to get these in Phnom Penh (for Dragon and Cathay) and Vancouver for Air Canada?

Thanks

Most likely they will all be separate; Dragon & Cathay are partners so maybe you will get those two, but my guess would be all separate boarding passes before each flight.
Are you concerned because of seat assignments or connection times?

You can get your AirCanada boarding pass online before you depart from Siem Reap.

... if that's within 24 hours of your AC flight time.

Thanks for replying everyone.

I am concerned about my connection time in Hong Kong, only 1 hr 35 min. Hopefully Dragon Air out of Phnom Penh is on time.

So, do I need to exit the secure/tranist areas and then go back through security after I get my boarding pass? I don't know if this matters but the entire route was booked together by my travel agent.

Thanks

You will go to the transfer desk at HKG, and not the regular check-in, to get your subsequent boarding pass to YVR. You will go through security but no immigration. [And since Dragonair is a fully-owned subsidiary of Cathay Pacific, you may already have a real BP issued for your CX flight.]

You have plenty of time for that connection in Hong Kong.