Maximum breaker on NMD7 8/3 wire?
In Canada, NMD 8/3 is allowed for up to a 40A circuit, NMD 6/3 is required for 50 A (Actually NMD 6/3 has an ampacity up to 55A, but try to find a 55A breaker…). Sorry, Eric.

Additional info: You may find some ampacity tables that list NMD8/3 as having an ampacity of 55A, but these tables assume a 90˚C conductor temp, and the code says you need to use the 75˚C ampacity when connecting to terminals rated to 75˚C, which includes all domestic circuit breakers and the NEMA 14-50 receptacles used for ranges and stoves.