Entering Canada north of Seattle is certainly an option. The eastern Summas/Abbotsford crossing is the most direct for drivers headed east.
Hwy 1, the Transcanada is the main highway across the country, and takes you to Banff. So it is well traveled, but like that California pass, it might be too busy for your taste.
At Hope, 1 turns north and follows the Fraiser River. No significant climbs, but as any road along a river it has curves, bridges, and some long views down. But the fast route out of Hope is Hwy 5, which climbs to a plateau around Merritt, followed by a drop to Kamloops. The initial climb on 5 is steeper than any US freeway, but trucks handle it fine.
After Revelstoke Hwy 1 crosses another pass as it goes through Glacier NP (the Canadian one), and other pass as it crosses from Yoho into Banff.
There's lots of great scenery this way, and good highway. But overall the route through Spokane is flatter.
Heading north out of California, US97 is a good alternative to I5. Most of it is on the east side of the Cascades at around 4-5000 ft. Overall it's as high as I5 on the CA/OR border, but the climb is gradual. Most of it is wide 2lane, not divided, but it is relatively flat and straight. There is a drop at the north end where it meets the Columbia River and I84.
