In Canada, every area code has at least one CO Code (or prefix) set aside for testing purposes. If you are looking for test numbers, these are the prefixes to scan, but be warned - you may not be able to access these prefixes outside their home area codes. If one prefix does not seem to be working, try another for your area code - some plant test codes are regional while others are area-code-wide.
Note that since our last update, Bell Canada has released the 320 and 999 prefixes which were formerly plant test codes in many Canadian area codes. Some have alreay been reassigned as geographic NXXs, those that have not may still contain test numbers.
If none of the exchanges for your area seems to respond, try a few numbers with 1 plus the area code then the number. Just because you have to dial "1" doesn't necessarily mean you will be charged for the call.
As with other prefixes, don't scan from home - there may be backdoors to 911, security and other numbers that you really don't want to be calling from home.
Suggestions (Where NXX is the prefix you are scanning):
And here are the test prefixes...
(2) 604-550 was formerly a plant test code; now the CNA lists its use as "routing." It may still contain test numbers.
(3) 902-811 was formerly a plant test code; now the CNA lists its use as "Reserved SAC." Switches may still recognize it however, and it may still contain test numbers.