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If it is a single-entry US visa the case falls under automatic visa revalidation, so your father will have the same period of admission (till Dec 30).
If it is a multi-entry visa, then, in theory, it counts as a new admission and a new period of admission will be given.
However, in practice, US CBP on Canadian border do not bother giving you a new entry stamp, so the period of admission will likely remain the same.
A possible way to extend the time would be travel from Canada, somewhere else (e.g. Iceland - shortest flight), re-enter either Canada or US and present yourself before US CBP for an admission
There is a perfectly legal way of extending your stay from within the US:by filing I-539