Map Reading .. essentially you go east to get to the back side of the Cascades,
then come back over them, again, to get to Vancouver BC.
East of the Dalles Oregon, US 97 cuts through the Yakima nations reservation, going generally North,
WA 20 comes west again further north, above the denser Seattle Metro Area.

Staying on US 97 the border crossing is Osoyoos BC .. then take Canadian routes back west to Van BC.
on my map, Allison pass shows it at 4,436', Canada

WA side, Rainy Pass on 20 is 4,855', Washington pass, 5,477' .