You need two Paypal accounts.
One uses your Canadian address, banking information and credit card.
The other uses your American address, banking information and credit card.
PP cannot handle addresses from different countries on the same account, although you can have multiple "gift" addresses from the same country on an account.
And a US dollar account on a Canadian bank doesn't count. This all has to do with US Treasury money-laundering legislation. It's not PP being the usual richards.