Sorry, in all the years I had a Visa through RBC Centura (at the time) then changed to RBC Bank USA, I have never had a problem using it online. The first few numbers do identify the issuer.

The only issue I have seen with certain online merchants (in North America, anyway) is if they will only take a billing address in the country where the site is located. For example, Drugstore.com will only let you use a card with a US-based billing address - there's no option to put in another one. So if you have a US-based card, but a Canadian billing address, it won't be accepted. Also, some airlines only let you book using a card with a billing address on the country's site you are using. i.e. booking a United ticket on their website through their US website will only let you use a card with a US-based billing address. If you select "Canada" as the billing address when making a purchase, you get re-directed to the Canadian site, and have to pay whatever the fare is in that locality (which at times can be cheaper or more expensive).

I am temporarily living in India now - which is a completely different situation - and many, if not most, websites here will not accept any foreign card - only Indian-issued debit/credit cards.