Quite a few countries hold "fifth freedom" rights between Canada and the US. Some of these rights are either unassigned to their airlines or unused by their airlines. The following are among the countries that have rights to carry fifth freedom passengers between Canada and the US:
Argentina, Belgium, Brazil, Bulgaria, Chile, Czech Republic, Denmark, Dominican Republic, Fiji, Germany, Greece, Ireland, Israel, Italy, Jamaica, Japan, Korea, Morocco, Netherlands, Norway, Pakistan, Philippines, Poland, Portugal, Romania, Russia, Saudi Arabia, Spain, Sweden, Venezuela.
There are quite a few...and most of them are either unassigned or unused.