India to Seattle (USA) via Vancouver (Canada)


I live in Seattle with my wife. My parents in India recently got both Canada and US (B2) tourist visas. I am planning to book their flight from India to Vancouver as those flights are way cheaper, and then bring them via road from Vancouver to Seattle. This will be their first visit to both these countries. What kind of immigration checks should they expect at both Vancouver airport and US border? What documents should they be carrying? What documents should I (with L1 US visa and Canada tourist visa) be carrying while going to receive them and back?
Is it fine that they say on the Canada airport that I am waiting outside the airport and they are just directly leaving for USA from airport directly ? And they will probably be back again sometime for sightseeing in Vancouver.
Also, I went to Vancouver few days back by road. While coming back, it was a really quick (~2 min) check for us. I am wondering it won’t be the same when I will be coming back from Canada airport back to US with them. I am expecting that they might ask us to stop and go to some other ‘main section’ where they will do US Airport level drilling and proper stamping. So, just wanted to know if somebody has an experience with that.