Twice in the Canberra's operational history has it been simultaneously used by opposing sides, though not in direct confirmation. In the Indo-Pakistan Wars of 1965 and 1971, Pakistan used Martin B-57 Canberras in the night intruder role against Indian targets while India used the B(I).58 interdictors against Pakistan.
In the 1982 Falklands War, Argentina used Canberra B.62s armed with bombs and rockets to attack British positions around Port Stanley after an abortive anti-ship mission resulted in one Canberra getting shot down by one of the HMS Invicible's Sea Harriers. British PR.9 Canberras operated covertly in the reconnaissance role by No.39 Squadron in Chilean markings to cover Argentinian military instillations and it is rumored, also the cruiser General Belgrano.
Source: English Electric Canberra, Warpaint Series No. 60 by Charles Starfrace. Warpaint Books, 2008, p72-75.