Hunter, Beaver above holds the key to the "when."
When Canada adopts the twin of the Sport Pilot license, a bilateral agreement would be quickly agreed on.
I suspect that on the Canadian side they don't want to admit Sport Pilots (and those flying under Sport Pilot rules) as that would be an admission that it is a viable option for pilots - effectively establishing domestic policy by the means of international diplomacy.
Plus this would be an issue ripe for petty political advantage, particularly in elections where there is little to differentiate parties or candidates. "So-and-so stands for loosening aviation safety to the danger of the regular citizen who can scarce afford the luxury and expense of owning an aircraft, many of which cost well over a million dollars. Vote for us and we won't abandon the duty of the government to keep you, and our Candian skies, safe."
I'm being cynical, of course.
It would be interesting to know how the bilateral agreement with the Bahamas was achieved.