I think Japan would be an even better comparison than Manchuria, given that this is supposed to be a country largely surrounded by water (or maybe the Korean peninsula if it's important to have that rainy season). I'm pretty sure rice was not really cultivated in Manchuria during historical times, though that is probably less true today.

@ the OP:
If possible I'd suggest moving the place farther towards either pole, any place below 30 degrees is bound to have a subtropical climate (you might get a little flurry of snow once in a decade or so) unless your planet is basically an ice ball with a severe ice age going on.