What borders Washington state in the north?

to the north of Washington state is the Canadian province of british Columbia

& you could also just say Canada or the Canadian border borders Washington state in the north

yet the state of Oregon might also be said to border Washington state in the north

in the sense of

to its own north

to the north of Oregon

& it is a peculiarity of English that one cant be positively sure which of these two meanings you have in mind

moreover it is a peculiarity of geography that regardless of which way you mean the question

the state of Idaho also borders Washington state in the north in a few places

due to the sinuosities of the snake river