Dog food is an issue coming into the US, but not into Canada.
We feed Ol'Roy Walmart food, but that didn't seem to matter, they confiscated it anyway on the US side.
But in recent years they have not been asking about dog food at our border crossing (going into Maine).
We have never been asked about it going into Canada.
Note that there are other items the US Customs don't like, fresh meat, tomatoes and other things.