but you don't have to accept this approach.
Your contract was with PC World, they sold you the printer, and under current consumer law they are liable to replace (or repair) the printer.
The law says that PC World must be allowed to repair the fault, but they must return it to you, fully working, within a "reasonable time". The law doesn't define "reasonable" in this context - each case is considered in isolation, should it come to court.
In the real world, companies like PC World can't usually repair things like printers or monitors, and in your interest they would tend to refer you directly to the manufacturer. They would have to do that themselves anyway, and by asking you to make direct contact they may well be saving you some time - a link will have been removed from the chain.
I think it's worth your while to write to PC World, formally rejecting the printer as being "not fit for the purpose for which it was sold" so that you have it on record. The fact that Canon have promised to get a technician to call you is a good sign - he/she will probably be able to authorise a replacement machine if that proves to be necessary.