For some reason, every time I tried to print CUPS was asking me for my username/password. This is fine when using applications which support this, and wasn’t enough of a hassle for me to bother with. Some applications however don’t have the capability to authenticate, and so it became an issue.

The solution is, however, trivial.
Open /etc/cups/printers.conf as root and comment out the line starting AuthInfoRequired like so:

<DefaultPrinter Canon>
#AuthInfoRequired username,password
Info This
Location Yes
...

then restart cups for the change to take effect.
On archlinux:
# /etc/rc.d/cups restart