As long as you have a valid US visa and a valid Canadian work Permit you won't have a problem going in and out US and Canada regardless travelling by air or driving I have done this a lot of times and once in a while you would be interrogated but its fine as long as you are honest I've been interrogated twice and one time for more than 2hrs but all these interrogations happen when entering US and is normal they randomly interrogates. But never have problem entering Canada...one time the US border took my WP and I'm worried that I can't enter Canada but hey everything is computerized now so i entered Canada without further questions.