Who's to say other countries credit ratings will fall more than Canada's? Credit ratings from Moodys, S+P, fitch etc signal to the debt issuer the rate they can reasonably expect to pay at auction on the debt.  If Canada's capacity to service its debt, or if Ontario needs federal help, the credit worthiness of canada will decline.  Canada hit a low of Moody's aa2 on prime paper in 1995 and finally rose to Aaa in 2003 where it remains. The difference in interest payments between those two ratings was $billions of dollars  every year.