On Basic and UltraBasic fares, the bag under the seat may be the only one you get, so it has to fit. A bag of 40 × 30 × 14 cm or smaller fits under the seat on every airline we track, including Air Canada (43 × 33 × 16 cm) and WestJet (41 × 33 × 14 cm).
Soft squashes, rigid doesn't
A soft bag that's slightly overstuffed squeezes into the space. A rigid one that's 2 cm too deep simply won't go. That's why we'd pick an under-seat travel backpack sized to the strictest limit: it opens like a suitcase so packing cubes fit, and a trolley strap lets it ride on a suitcase handle through the airport.
Bringing a laptop
A slim laptop backpack that takes a 15–16 inch laptop and stays under 15 cm deep is the one to look for. Put the laptop sleeve against your back so it slides out quickly at security, and pick water-resistant fabric for rainy transfers.
A weekend in one bag
For two or three nights, a soft under-seat duffel is surprisingly roomy, and it's the natural fit for Flair, Porter and Basic fares on Air Canada and WestJet. Small packing cubes make the most of the space, come out in one go at security, and keep a change of clothes ready if you're also checking a bag that gets delayed.
The gate is where it costs you
If you're on a Basic fare and turn up with a full carry-on, expect a fee to check it at the gate. Test your bag with our carry-on size checker before you go; the table below shows each airline's limit.