I think connecting in any Canadian airport is a pain when traveling to the U.S.
 

Not sure if this is the right place to post this (Mods can move) but my last week travel involved YYZ-YVR-OGG-SFO-YYZ on AC and UA so not sure to post here or in the YVR thread.
I have flown to Hawaii three years in a row. Via Calgary, SFO, LAX and YVR. I think connecting in any Canadian airport is a PIA. Last weeks trip involved security at YVR, no Nexus line, random checks, all electronic equipment out, followed by US CBP with just one GE machine. At least the YVR airport is nice other than the expensive duty free. And their propensity to either not have a Nexus line or send everyone to the Nexus line.
In comparison flying thru US airports, you just do security and US CBP in YYZ and just change planes in LAX/SFO. Ditto on the way back, security at checkin at OGG and Canada customs/Nexus at YYZ.
Not sure why US needs security again when connecting airside from another Canadian airport.

The title should read: "Connecting in any Canadian airport is a pain when travelling to a destination in the U.S.". With that statement, I'd agree, because if you connect in a U.S. airport you save yourself the entire re-security circus.

Now, if your choice is LHR-YYZ-EZE vs. LHR-JFK-EZE, the Canadian airpor transfer is much smoother than the U.S. equivalent.

I connect to other flights at a US airport flying in from YYZ. I never had to go through security again. Just once before CBP at YYZ and I am done.

YYZ YVR OGG is not an airside transit as you need to enter the US CP area landside. You need to re-clear security for Y?? YYZ USA connections.

The US has a different security standard than anywhere else. To access a US flight in Canada, you are going through special security, not regular CATSA screening, even though it is done by CATSA. Once you are in the sterile area of a US airport, you will not normally need to be screened again.

IIRC there is a handful of CDN airports without Pre; YYJ comes to mind. And AC does fly there nonstop from YYZ ;)

Probably not helpful for OP, though there are some odd non daily flights ex YYJ, including seasonal OGG if memory serves right, though it's possible I just dreamed it ....

Huh ? Connecting in YVR to OGG was definitely airside. There is a seperate area to get to US CBP and it is airside except you have to do security all over again

Sounds like semantics - I fly YYJ-YVR-US all the time (to avoid Devil's Chariot on YYJ-SFO even if it adds time / connection to my journey - OK, usually, taking this in a couple of weeks :( ).

You indeed get off the plane at YVR, go to US Pre, go through Immigration / Customs and then clear US security having cleared Canadian security at originating airport, all airside without ever exiting terminal.

IME, CATSA is more of a hassle than TSA without pre, US bound or not.

You are still at the same CBP checkpoint as the landside passengers.

Yes, for CBP. But the security check (CATSA) is from the airside transit before it spills you out into CBP.

Connecting anywhere to go to the US is a pain

The question might come down to "Who is making the airside connection to the US". I'm not familiar with YVR but at YYZ (T1 at least) the connecting passengers going through the special airside screening before US CBP are from both D (domestic) AND E (intl) arrivals. A passenger coming from, for example, Istanbul needs to be rescreened in N. America before boarding another flight and YYZ is not set up to separate them from someone coming from Ottawa or wherever. Still, it's a good system.