This seems such an obvious problem I am not sure why I have not had it before or why I can't find a simple solution to it.

I have a Scott CX Comp bike fitted with Tektro cantilever brakes. After recently servicing the bike (and adjusting the brakes), I find now that the brakes come on slightly when turning the front wheel. The cables are exerting some force onto the brake cables and causing them to come on slightly. It makes the bike pretty noisy. I can loosen off the brakes a bit to avoid this, but think that there must be a way to get around it. On the front brake, in particular, it is pretty bad as the cables push on the front brake cable as it drops into the straddle cable guide. The brake cables are fed along the bars and taped over in a conventional manner.

Any ideas?

First try removing the front brake cable from the pinch bolt at the brake, pull the housing and cable out of the spaghetti bowl of housings, and reroute as simply as you can.

You should be able to rotate the handlebars fully without affecting braking or shifting. If the rear brake is applied at one extreme, the housing is too short. This is not uncommon, and it's a little more work to fix.

Thanks, Andrew. I'll give it a try and see how I get on. The rear brake is certainly not as big a problem as the front, but does still rub when the wheel is turned significantly.

Turned how significantly? In normal riding you turn the bars very little. If the brakes do not rub in normal riding/turning there is no need to fix them.

I first noticed it when cornering normally, but simply thought that it was my brakes had been adjusted too tightly. As mentioned, I have recently serviced the bike including adjusting brakes and cleaning rims. Then when investigating it more, I realised that noise appeared to be coming from the back brake as well as the front when cornering. I have since loosened off the brakes slightly as I discovered the problem with the cables when I had the bike up on a stand.

I have yet to try the bike on the road to see if there is any noise during normal cornering.

I accept the point that you move the front wheel very little in normal circumstances, but there are occasions when you do need to do this for negotiating sharp turns through gates, traffic, etc.

Most often, this means that the cables and housings are too short.