Can you ask "Mandarin or Cantonese" instead of "Chinese"?

it is definitely not rude but from experience overseas chinese are very hit and miss in regards to friendliness. i have tried speaking to many chinese people in my town, some went great and some went terrible lol. but you should definitely try it.

I would just wait until you have learned enough Mandarin to the point of where you can differentiate the two. there are many videos on the subject of the tonal differences and once you learn enough Mandarin it will become glaringly obvious