Not sure what you like to shoot, But I would bring the 17-55, that is one great lens and the 70-200 also a great lens. I do like landscapes , or to isolate the subject hence my two picks.
I'll second the above but would also bring the 18-135mm. It is the lens that spends the most time on my 80D and really isn't going to add much in weight or space taken up. Great jack of all trades but the other two lenses cover you for anything special.
Not sure your comment about less is better when crossing the border, unless you are just flat out unlucky they never go through stuff and you only declare what you bought north of the border when you come back south. Being in the Seattle area, I cross the border 2 or 3 times a year.
Side note - where in Canada and where are you crossing?









