Steve,
Only for future reference, i would like to post some stuff i've learned while doing some research on this
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Paypal IPN allows you to pay with your paypal account first. If you don't have enough money then it uses your
primary credit card (associated to your account). Seems to me it doesn't allow credit card payments directly
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Paypal Express seems to work pretty much the same
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Paypal Pro lets you integrate the credit card payments directly into your website, however it works only for the US
(confirmed by Paypal support)
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Authorize.net works both for the US and Canada (also confirmed)
please feel free to edit my post if i made a mistake, this might be useful for some other developer
thanks for all your help, i'll go with the authorize.net option this time
best regards
Fernando Gabrieli