try this for the rules:
Total Number of Items >0;
AND SubTotal of Items <=$99.99 (changed from >= $100.00)
AND If Session Variable Exists: eCartCheckoutForm_shipping_country
AND Custom Condition:
(($_SESSION['eCartCheckoutForm_shipping_country'] == "US") || ($_SESSION['eCartCheckoutForm_shipping_country'] == "CA"))
The calculation is Flat Rate = $8
The second rule ($20 for all but CA or US) is:
Total Number of Items >0;
AND SubTotal of Items <= $99.99
AND If Session Variable Exists: eCartCheckoutForm_shipping_country
AND Custom Condition:
(($_SESSION['eCartCheckoutForm_shipping_country'] != "US") && ($_SESSION['eCartCheckoutForm_shipping_country'] != "CA"))
The calculation is Flat Rate = $20