Why are you fiddling with eBay as far as a second address? That's something you can deal directly with the seller or add it in PayPal if you are paying that way. (maybe I'm missing something?). When I've had purchases shipped to an alternate US address I just add it when making my payment (by PayPal mostly).
As for bringing commercial shipments back in your "trunk" should not be a problem. It's been YEARS since I've done it (at Fort Erie), in "olden times" (pre-computerization) it took several hours after you submitted the paperwork to get a release but I expect that it runs MUCH faster now if the speed at which one-off shipments are now cleared at Pearson is any indicator. Unlike going into the USA doing the paperwork yourself is pretty easy even if it's a very high value shipment. Customs should help you the first time through and after that it's really just a matter of copying the forms and changing the values. Once you know how to create a "Customs Invoice" and complete a B3 form you can do the paperwork in 5 - 10 minutes and probably wait perhaps 30 minutes for your release.
Back in the day it was cash or certified cheque only but you should be able to pay with a credit card now.
All the info you need can be found here:
http://www.cbsa-asfc.gc.ca/import/acc-resp-eng.html
If it sounds complicated...it isn't!

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
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