His being adopted had to have been established season 1, because that’s the only season I watched.
Negative. It was established in “Ike’s Wee-Wee” that Ike was adopted. That was in the second season. I’ve been watching South Park since the beginning and have seen every episode in the order in which it was aired. There was nothing before this episode that established Ike as being Canadian.
Yeah, I remember it was a surprise to Kyle and all his friends that Ike was adopted. So I don’t think we the viewer would have any way of knowing either.