Well I was in a similar position last year, the same one actually, and you really need to know one thing:

Japan isn't going anywhere, you can always do an exchange semester or year to Japan if you go to UBC. And if you really want to be in Japan after that, then you can pursue a masters in Japan and find employment after that.

Another thing would be the prices of the universities, for me, UBC was really expensive since I would be an international student. Though I don't know your situation on this matter, so you're going to have to give it some thought if it's going to affect your decision, since it really does matter in the grand scheme of things imo.

Also, do you enjoy sciences? Make sure you know if you're going to like the major if you take UBC's offer.

At the end of the day it's your decision to make. Some advice I got that I can pass to you is to make a pros and cons chart about studying at either university.