The trademark opposition process varies from country to country.
In Canada, trademarks may be opposed within 60 days after publication in a special Trademark Journal. Any party that believes that it may be damaged by the registration of a trademark, may file an opposition. Oppositions in Canada are handled by Trademark Opposition Board. It is an administrative procedure that is relatively inexpensive. It’s the cheapest way from stopping a trademark from being registered.
If a trademark was not opposed, it will register. If you missed an opposition deadline, the only way to challenge a trademark is to go to Federal Court (an expensive and very long process).
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