Can citrus cause canker sores?

NO!!! But any acidic materiel will sting on contact with an aphthous ulcer, suddenly making you aware of it.
Yes. The acidity in the citrus can affect the ph in the mouth that can cause canker sores in susceptible individuals.
Sorta. Anythig acidic like citrus can trigger an outbreak. I say 'sorta' because it is triggering an outbreak of a virus that is already there. Trauma like biting your tongue or a lot ofmstretchingnat the corners of the mouth at the dentist can also trigger outbreaks. Back on the food note, i've also seen tomato-based products trigger outbreaks as well.
Canker sores. The cause of canker sores is uncertain, but some people seem prone to developing them with large citrus intake. Most common cause is mouth trauma, as from overly vigorous brushing the teeth or accidentally biting the inside of one's mouth. Try limiting citrus intake to see if that makes a difference.