Admissions About G30 Program

Hello everyone, thanks for any helps in advance!

I am currently achieving a bachelor degree at a Canadian university in second year mathematics and statistics, and considering to apply for a master program in Japan; I am familiar with Japanese N1 and the fact that G30 is an English taught program, however, may I please come to clarify some other important questions:

i) I am planning to go for information technology field, mainly as data science. How hard would the admission be for G30, if I wish to aim for places. from The University of Tokyo and Kyoto University, to Waseda University and Keio University?

ii) At this moment I am very confused with the information from surroundings: Some have said Japanese universities for master programs don't care about the grades throughout university and such, only the entrance exam matters; some, on the other hand, have said something completely opposite.

For some personal reasons I prefer Japanese universities. These are the two main questions in my mind initially and temporarily.

Any helps would be very much appreciated! Thank you again for your time!

Best,
Joseph

generally speaking, in master programs in Japan, they don't teach you from the beginning and you will be treated as a beginner of researcher, specialist,. it means they expect that you already have fundamental knowledge. (i.e. undergraduate is beginner program. )
many of applicants for graduate school have already decided what field they want to study "deeply" and the professor who will be a mentor.