It is possible to find the postal code of a homeowner on Canada 411 with just a name. However, in many cases, it requires more information than just a name.
If the homeowner in question has a unique name, then that may be all that is required to locate his postal code. If the name is more common, then at least the province is required to narrow down the list of people. If the name is common enough, Canada 411 doesn't even generate a list without more information to narrow things down. Extremely common names may even require the town and the province of residence to get the desired postal code.