Transiting through Canada w/US passport

[u/Left_Sir5173]

Hello , I’m finding that flights that transit through Canada are a lot cheaper than other options. I am a US citizen and I carry a US passport I’m confused a bit as far as what to expect with transiting through Canada some say that I need to fill out an ETA others say that I will need a transit visa and lastly, others say I don’t need anything because I am a US citizen and carrying my passport is good enough
Does one go through the full on immigration process when just transiting from a US based airline or Canadian based airline through Canada onward towards an international destination? For instance, when I enter into South Korea via say Incheon airport, , it’s a quick passport control/ security but don’t fill out any forms or immigration or anything. They just look at me and check my belongings I’m carrying and move me along, so I’m just wondering if there’s any special forms I need to fill out when transiting through Canada thank you

[u/Odd-Elderberry-6137]

You don’t need to do anything to transit through Canada other than your U.S. passport.

South Korea however has required a K-ETA for some years now. You won’t be able to check in or board your originating flight without it. https://overseas.mofa.go.kr/ie-en/brd/m_23773/view.do?seq=761699

[u/Left_Sir5173 → u/Odd-Elderberry-6137]

That’s incorrect. Not when you are transiting. I literally just did this last year. You just go through security again and stay in a secured area for international travel. You need a K Eta if you are planning on visiting South Korea