I own a 50 year old house in Eastern Canada. My house always had a
slight seepage in the basement. Not significant to cause an alarm but
annyoing enough to prompt me to do something about it.

Yesterday I pryed off old "finishing" (essentially plywood nailed to
framing studs) and discovered a hole in the basement wall. The hole is
wide an shallow. I'd say about 1.5" wide and about 3/4" high. I'm
fairly sure now that this hole is the source of my seepage. Like I
said, the seepage was never significant so the presence of the hole
could easily have caused it. I can't verify whether the hole goes to
the outside but it is at least five inches deep as I could stick my
entire finger in it. I suspect the hole goes all the way through the
wall.

My question is this. What caused the hole to appear in the first place?
Could it have eroded? It does not seem likely to me as the edges of the
hole seem quite sharp.

Is if realistic that the hole was gnawed by a norway rat or another
type of rodent? We had some rat-like poop in the basement but not near
the hole.