Setting up Canti Brakes with Shimano 105 5700 STI's in the front

Not an issue with the sti and canti's, try missing out the gear cable guides on the headtube, perhaps run the rd gear cable on the left side of the frame and cross the wires under the downtube
also a few pictures of the side view, top and direct front would help to give a better idea of how the cables are flowing, it looks really messy and crossed (but that might be to do with left hand/rear brake set up, stumpy cable hanger or cable length)

Yes. Miss out the guide and shorten the outer so it doesn't foul. Should be fine.