If the buyer has two physical adresseses entered on ebay, and sets the USA one to be default BIDDING address, yes, they can bid on your items. It is nice to be able to setup like that because I want all heavy items (boxes, cases, etc) shipped to my USA address (as well as sellers who won't ship to my Canada address) but I also want to be able to get shipped to my Canada address by doing the "request total" to checkout with Canada address.
It can get a bit annoying for the seller because they will invoice me at my USA address, only to have me turnaround and request total and the new invoice must have shipping method international set or I cannot checkout on the item.
Since I have to pay $5 per item to my USA parcel depot, I would rather just get singles and small envelopes sent direct to me in Canada, even if it is $7 or $8 shipping compared to $2 within USA. By the time I add my depot fee and possibly GST and PST crossing back over the border, I'd rather just get it shipped to Winnipeg. Now, for the large items, it is sometimes more like $12 shipping inside USA and $50 or more shipping to Canada. You can see why I use a parcel depot for those type of items.
Both of my addresses are confirmed/verified addresses with PayPal to protect both seller and buyer.