This was the usual state of affairs until about November 2005, then the problem was resolved.
with the latest update of united.com, the problem as returned. Booking on
www.united.ca simply redirects to
www.united.com at the payment phase, and as you discovered, it defaults to US country code and declines payment as a result.
I do a 'book and hold' on
www.united.com and call reservations; make sure that they waive the $15 fee when you ticket - I've been charged twice already since Jan 1st and have had to ask for a refund.
I've already logged this complaint and will speak to the station manager at my home airport again this week - the ticket agents were getting really tired of me coming in person to ticket, and I had a long conversation with the station manager as to WHY I had to ticket in person.