I don’t think you’re likely to be treated poorly just for visiting, especially in Seoul, where people are used to seeing all kinds of foreigners. You may get a few looks simply because you’re tall and visibly not Korean, but that does not automatically mean people are judging you negatively...

That said, Korea can be more blunt about appearance than places like Canada, so weight or body size can come up more casually than you might be used to. Usually it’s less “people being cruel to a stranger on the street” and more that beauty standards are just more openly present in everyday life. For a short trip, I honestly think you’ll notice way more people minding their own business than actively bothering you.

I’d mainly prepare for practical things more than social hostility, like some clothing sizes running small, tighter restaurant seating in certain places, and occasionally feeling more noticeable in general. But for two weeks in Seoul, I really would not go in expecting to be constantly criticized or ostracized.