My cat Sprinkles and I makes a few 3-4 hour flights every year.
At least in the US, you need to get a certificate from your vet stating that the cat is healthy to travel. It has to be dated within 10 days of your flight. I don’t know if this is the same in Canada.
Before every flight, Sprinkles enjoys treats laced with kitty knock-out drops, prescribed and dosed by the vet. They help her be a bit more calm/a bit less yowl-y during the flight. She is a constant meow-er in cars, so before our first trip, I had visions of exasperated passengers tossing us out of the plane at 30,000 feet. Now, she usually meows a little bit once we have landed and are exiting the plane, but is very quiet once she is safely stowed under the seat. Usually, most people don’t even realize there was a cat on the plane until we are getting ready to deboard.
In the US, when you go through security, they make you take your cat out of the bag, and then physically carry the cat through the metal detector. Then you have to wait at the end of the baggage scan for the kitty carrier to make its way through, and hope that some non-power-tripping TSA agent will prop open the bag for you so you can shove your pet back inside. I was completely NOT expecting this the first time - I had figured the cat and bag would all go through the x-ray machine together. Normally, Sprinkles doesn’t tolerate being held any longer than she wants to be, but in the airport, with some sedation, she is either very calm or freaked out to the point of immobility, and still and has not yet tried to escape from my arms.
We have a soft-sided carrier which fits underneath the seat. I always try to get an aisle seat, especially if traveling with a cat - it makes everything easier when you don’t have to squeeze past two people with a cat and a carry-on.
We have never made a long a trek as you are planning, and never had to deal with a layover, though, so I don’t have any advice for longer flights.
TLDR: check if you need a vet certificate for pet travel; sedatives (not catnip) prescribed by your vet specifically for pet travel is good; a soft carrier is fine; be prepared to carry Yolk through security.
Good Luck!
love
yams!!
Edited to add: And make sure to tell the airlines you are traveling with a cat BEFORE you show up at the airport! Many airlines have limits of the number of pets they will allow in the cabin.