Austrian is part of the Lufthansa group, by some measures Europe's biggest, with Ryanair close behind. Lufthansa charges for seat selection as do many of the international carriers and most budget lines, so it is no surprise that Austrian would too. It's becoming more an more common, including on international travel by Air Canada.
I don't know exactly what you mean by VISA since the word applies to credit cards and to government visa documents. You can check Lufthansa procedures here: https://www.lufthansa.com/ca/en/check-in
Canadians can enter both Austria and Spain without an advance visa; it's part of the scrutiny of your passport at the border entry. If I remember correctly, that's what Ryanair looks at too, probably to protect itself. But it does add an extra step to flying on Ryanair.
I am surprise that you have found a cheaper flight on the route than Ryanair, always allowing that it hides various extra charges to pop up during the booking procedure. Congrats.
Whoever you fly with, checking in on-line, and printing out boarding passes if possible, is always wise and, with Ryanair, far less expensive than the charge at the airport. Printing the passes if you are at a hotel may be possible; consult the hotel reception.
