A note on duty: We have Free Trade which normally means no duty on most items. What you should expect to pay if you bring it back across the border yourself is the taxes. For folks in ontario, that'd generally be just the GST and PST. I've brought both computer equipment and books across the border (and other items) for years now and have never paid 'duty'. But I always declare my stuff at the border and pay the taxes. The last thing I'd do is try and sneak it across - if it's not worth the 15% then it's not worth my getting it in from the US. (just IMO).
I still use mailboxes etc in niagara falls/buffalo; I keep a mailbox there. They will mail stuff across from my box when requested, not sure what the charge is but it's not much. They do also take one up shipments I believe; certainly they used to. The phone number for them is on a previous page of this thread. Alternatively you could call ahead to them to setup a one time shipment, the drive down to pick it up - clear it at the border and pay your 15%.
Failing that, if you're getting something shipped, use postal service not UPS. What many people see as 'duty' with UPS shipments isn't duty, it's a whole ton of service charges for 'clearing customs paperwork', service fees for having to pay the GST on your behalf, stuff like that. And their rates are obscene (like $50 on a $100) - but again it's not duty, it's charged by UPS. If you ship post, they generally charge like $5 to clear the paperwork plus the taxes, and that's it.