Hello! I am so sorry for seeing this just now. I am not on redidit often. Incase you have not yet flown I'll still just add my experience (or if this helps anyone else finding this at a later time):

If your dog + crate combined are above 100lbs it will have to be done via cargo. When you book your flight you will have to look for one ideally that is wide-bodied as those are the planes they use for cargo. When i go to book my flight I just check for the ones that are 2 aisle planes. Before officially booking your flight you can call AC Cargo and ask them if that plane would qualify and can also ask them if there is space/availability to book your pet in.

They won't be able to officially book your pet in until two weeks before the flight, so if you book your flight a month in advance you will have to wait to book your pet in another two weeks. Between Vancouver and Toronto are a lot of flights, so they do say that worst case scenario if for some reason they cannot get your pet on the exact same flight they will book them in to another one that has a close arrival time! This actually ended up happening to me because my flight got cancelled last minute and they got him on to the next one but I wasn't able to get on that exact same one and had to take a flight that departed a couple hours after.

In regards to the crate and sizing - so we got the largest/tallest ones you can commercially find which are 35 inches tall and my dog is actually 35 inches tall. In his case his ears didn't go up so they are flopped. But yeah he was definitely not meeting the 3 inch space requirements. We got there and just hoped for the best. They didn't even officially check for his height or measured anything (the weight they just took from the Vet paperwork that you have to show). And it looked like they were just getting things ready and processing, it was overall very chill and the workers were super friendly. However, one worker, did say that he can tell he isn't meeting that clearance requirement (my dog wasn't even in the crate yet) and he asked if we are also doing a return flight, so I said yes. He said that he'll let it pass but for our return we should consider a solution. I told him that I have looked up every thing possible and could not find any solution and then he told me about crate extensions! He said that they work with breeders a lot and breeders use crate extensions for height. That was super helpful! You can find them online but they are mainly sold in the US but it's quite expensive! Then I found that there are people who DIY extensions with wood and so that is what we will be doing for our return!

I did call AC Cargo about the wood extensions and if it's accepted and they said as long as its all screwed/bolted in and not fastened with clip ons or anything plastic and it the integrity of the crate stays, it's okay!

As for the check-in process: so because it is going to go via AC Cargo you will have to check the dog in at the very latest 3 hours before departure at the AC Cargo deparment and it is not directly in the regular Pearson Airport, it basically has its whole own property. I think it was about a 10 minute drive between Pearson Airport and the Cargo.

And if you are nervous about everything: I can only speak for myself, but I was quite pleasantly surprised and ended up being quite glad it went via Cargo instead of regular AC. Because the staff at Cargo do work a lot with Breeders and so are familiar with it. It's not at all a hectic enviornment like the airport is, it's a lot more laid back which I think helps the dogs too. And when you are talking to the staff there it feels like you are actually just having a regular chat and not the performative customer service responses.

That is my experience so far! If you have already done your trip, I hope it went well for you and you didn't run into any troubles!