Hi Kevin,
The ebay.com is actually the US site. I've walked the problems and issues with listing to other countries when origin/location of an item is elsewhere, and it has some very tricky issues.
I know there is alot of confusion about International selling and ebay has even upped the confusion factor with a "new fee" for cross listing to aid "visibility".
IMO, listing on your "home" server with, in this case ebay.ca, with shipping to your selected countries, e.g. US, UK, will have your listing appear in CA (home), US, and UK servers. That's always been the case, as your items are available to bid where you live and where you'll ship to. ebay has a new fee to increase visibility in search for you items showing in other country servers, which we're all still trying to unravel. That fee was for US, UK, and CA, to start.
Listing to ebay.ca also gives you shipping origin and services for CA. The problem I've previously seen, is you won't have selections for your Canadian shipping services, like Canada Post, on the lister. That's because the lister assumes you're shipping from the country you're listing from.
Are there work-arounds for all the problems. Yes, but they may be less and less attractive with many of the new ebay policies, e.g. you could give the shipping costs in the description and explain that the item is actually located in Canada. Do you think bidders will like or understand (many don't read), that an item they bid in US is being shippped from Canada?
Again IMO, the simple method to get you going, is list in CA with shipping to US, UK.... and that will at least open it to international bidders.
Oh...and I should mention, I've shipped to all the lower Provinces of CA, UK, Germany, Japan, Mexico, and Chile by listing in US and offering international shipping. It does work.
Danno