It takes about 20mins to get to the border from Richmond, then if there is no long line ups you can pretty much get through within half an hour. Then from Mt Baker exit off of I5, it's another 45mins to the top of Baker.
Of course, if there is no dangerous killer crossing border alert, you should be able to come back at the same time as you have left Canada. Good Luck!!
Make sure you do make it back for the BBQ!!!