hmm, we are all forgetting one major factor...the longbowmen. England fought a full unit of french knights(calvary and infantry) and the longbowmen literally tore their ranks apart...then when the knights got in close, the bowman attacked with knives...
but, i think it would come down to strategy in an even numbered of army battle. Remember when hannibal attacked a city outside rome and the romans sent 70k troops to the carthage(and allies) 50k? well, if a good stratigest was on the field, it would be a tough battle.
i think that it is a near impossible scenario though. Because if it was midiveal japn vs midiveal europe, the numbers would DEFINITLY be in eruopes side and there is the chruch, if they called japan a great scourge, the europeans would rally vs japan.