What would be really interesting is seeing if Canadians can use the UK as well as the US store? Elsewhere someone commented that as a Canadian they suddenly cannot buy some books from the US store. The usual reason for this is because these are books where the UK publisher holds the Canadian rights not the US one. If that's the case, Canadian customers should be allowed to use both stores, but only buy a subset from each.
It would be really interesting to find out if this is the case.