Getting across the border is the easy part - getting healthcare, a drivers license, a job etc would be the hard part. Those are much easier to pull off sneaking in to the US than Canada.

You can do it accidentally in a few towns and I've crossed the US-CA border into the states before where we had to wake up the border guard.

There are many places in Washington state where one can walk (or dance) into Canada. Rather un-guarded border.