The Answer
Canadian Thanksgiving preceded American Thanksgiving by a little over 40 years. (sort of)
While Thanksgiving in Canada is celebrated a month and a half earlier in mid-October, this is not what we mean by “who celebrated Thanksgiving first”. Instead we’re looking for the answer to which country celebrated Thanksgiving before the other, historically.
The answer here comes from a recent article by National Geographic. According to the article, the tradition of celebrating Thanksgiving in Canada began in modern-day Newfoundland in the 16th century, more than 4 decades before the famous “first” Thanksgiving in 1621 in Plymouth, Massachusetts.
Canadian Thanksgiving kicked off with a feast of biscuits, salt beef, and mushy peas in 1578. That’s when Sir Martin Frobisher sailed from England in search of the Northwest Passage.
In New France (modern-day Quebec), huge feasts of Thanksgiving were held between the Mi’kmaq and the French as early as 1606.
To be fair – neither Canada nor the United States of America existed in the 15th and 16th centuries, so technically these ‘first’ Thanksgiving celebrations were neither Canadian nor American. And to be even more fair – the local indigenous populations had been celebrating harvest feasts well before either of these, so the correct answer might be that neither is first.