when you ran the checkout wizard in eCart, you would have had to select whether the checkout should use PayPal Payments Standard or PayPal Payments Pro.
MyQuestion is: which of these options did you choose?
it sounds to me like you probably choose PayPal Payments Standard. if that is the case, on the confirm page, find the following line of code:
<input type="hidden" name="currency_code" id="currency_code" value="USD" />
and change it to:
<input type="hidden" name="currency_code" id="currency_code" value="CAD" />