I just completed a trouble-free train ticket purchase on Trenitalia.com with a CIBC credit card. You do need to be signed up for a password with Verified by Visa. I will report success to The Man in Seat 61, who is keeping track of which bank's cards succeed or fail. But I thought there might be other Canadians here who would be interested.
Has anyone else tried or failed? Post here and email to seat61.com. I'm happy to provide tips if you are trying this for yourself, but The Man (seat61) has detailed screen shots and instructions online.