Flying YYZ-ICN-SGN on AC and Asiana. Showing a 1 hour connection between the AC flight and the Asiana flight. It's a legal connection, but is it a safe one assuming YYZ-ICN flight is on time?

Presume you are connecting to the 7:30 PM flight. You should be OK, but if you miss it that is the last flight of the
day. You will have to wait until 7:30 AM for the next one. The usual - if AC is on time, you'll be fine. If they are late,
you will be 12 hours late into SGN.

ICN isn't a terribly complex international airport... it's awful, but in terms of transfers it's fine.

Both AC and Asiana are at Terminal 1. I am pretty sure your AC flight will use one of the arrival gate 1-50. Departure gates 1-50 are also used by Asiana (see this Terminal 1 map). Once you deplane, locating the transfer area entrance should be easy and security would not take too long. Expect around 15-30 minutes to reach the boarding gate for your ICN-SGN flight.

Why do you call ICN an awful airport? Please tell us more.

Also I don't understand that. Took Korean last year for the very first time and I actually enjoyed the airport experience. Enjoyed it enough that my next flight to Asia is actually via ICN with 23:45hrs stopover. The airport is easy to navigate, straight forward and well marked.

Generally I found it massively underwhelming. I had a 14 hour layover but left something on the plane so ended up waiting nearly an hour only to be told it definitely wasn't where I said it was (I know it was, I remember putting it there "for safe keeping"). So far so crappy, but equally that was Lufthansa in Korea not ICN. I got a cab to eat and watch a (Landers) baseball game in Incheon which was genuinely fun and when I started to flag around the 7th inning went back to the airport. It was overcrowded, food choices were minimal/disappointing (and slammed) and overall it gave "budget airline airport" vibes for the 3-4 hours I had before heading to the gate. Part of the issue, I suspect, is that I was expecting it to be like Changi (modern Asian hub with all that comes with that) and in my tired state (30 hours awake) the disappointment coloured the experience. If I'd had a few hours to get a snack and get back on the next plane I may have had a different experience. It was pretty efficient but that didn't change the "feel".

I'd go through again, but try to minimise my time at the airport.

I've transferred here multiple times, and it's awful. Much of that awfulness comes from transfer security which ranges from not great to horrific. We've almost never cleared transfer security without some kind of issue - being completely confused by a small plastic ziplock bag of coins with multiple passes of the bag through the x-ray machine as if they never saw coins before in their lives, dumping an entire suitcase because of a toe-nail clipper while holding it up and saying "dangerous", staring at documents before the x-ray for multiple minutes per passenger like an archaeologist examining the Dead Sea Scrolls, keeping the transfer security room as hot as possible during summer to the point of almost passing out, arguing over my medication bottle, then x-raying it 3 times before finally dropping it on the floor and letting it roll around until I told them to just throw it out at that point, and my personal favorite, asking an airport information person where the lounge was, and being told "Gate 25", then walking over to Gate 25 and finding no lounge, then walking back to ask her again "but you said it's at Gate 25", only to be dismissed with "I said it was NEAR Gate 25", which apparently meant a 5 minute walk from Gate 25.

If an airport was one of those Halloween haunted houses where scary things jump out in front of you, it would be ICN.

Maybe this is a T1 thing? And I do see that OP is on a *A itinerary.

But for what it's worth I have connected at ICN multiple times on SkyTeam and my only complaint about T2 is that even neighboring gates feel far apart as if they saw the need to cram in as much shopping as possible, so it makes for some long walks. But the facilities in T2 are perfectly fine and I have never had any issues clearing transfer security there, quick and painless every time.

I certainly don�t have the same definition of an awful airport

Yes, I have nothing but praise for ICN.
My only "bad" experience in over 100 trips through was the one time they wanted to search my luggage after
passing through the Xray machine. It appears that 7-8 paperbacks looks like stacks of currency to the
X-ray reader.
My most memorable praise-worthy experience was the time I left the book I was reading on the airport limo
bus to the airport, and the lounge staff traced the bus/driver, and had the book returned to me pre-flight
in the lounge.

I suppose it was Sky Hub Lounge East, which is often to be said close to Gate 25 but the entrance on the third floor is actually closer to Gate 11. This lounge map for Incheon Airport Terminal 1 provides locations of all lounges at Terminal 1, which might be useful for others with connecting flight at T1.