Coming from Seattle you will cross into Canada a one of 4 border crossings.I would recommend the Sumas crossing that will get you to Hwy 1 faster without alot of traffic.
Hwy 1 is 4 lane to hope BC and then turns to 2 lane through the Fraser Canyon. If you take the Coquhalla hwy #5 form Hope it is 4 lane all the way to Kamloops and it re connects to Hwy 1. There are some high mountain passes but it should be no problem this time of the year. Hwy 1 will take you through Banff National Park which is very scenic before you get to Calgary.
I hope this helps.