... customs...
I am a camera operator and D.O.P. and occassionally work across the border and take equipment / gear with me. I take a list of all my gear, along with dollar values. Stop in at the Canadian office with the list ... they will copy and stamp it up for you and give you some paperwork. (I've never had them come and check the stuff in my van, but I suppose they could if they wanted). For a pleasure trip, I'm sure that's all you would need to do, but for work I have to stop at the U.S. office with the same list, where the U.S. customs guys run my ID, grill me a bit, try to intimidate me, sometimes threaten me, and attempt to get me to admit that I'm either: a)stealing work from god-fearing americans; b)smuggling bc pot; c)an al quaeda operative; or d)working for some goddam leftie/commie documentary out to make america look bad on the telly-vision ...
But as far as it goes, I really wouldn't sweat taking your laptop back and forth... they are pretty ubiquitous items these days, and there's no reason for canada customs to assume that you're trying to rip them off. Given the fact that your laptop is 2 years old, it probably shows signs of wear and tear, and contains plenty of your personal documents and whatnot to prove that it's yours.
... in fact, I made a trip to oregon last summer for the sole purpose of picking up a tax-free, american-priced powerbook ... I mailed the box, documentation and stuff back to canada and came across with the laptop on the front seat of my van... no questions asked.