Americans gained their Independence before Canada did, but Canada celebrated Thanksgiving a long time before the US. Canada can go back as far as 1578 for their first recorded Thanksgiving, while the United States had theirs at Plymouth in 1621.
The U.S. celebrates the 4th Thursday of November, Canadians the 2nd Monday of October.
Martin Frobisher was said to have had a feast of thanks for safe passage, in Nunavut, on his 3rd exploration, after losimg a ship in travel. In Plymouth, U.S. invaders or explorers had their first feast with the Native Americans around 43 years later.
It took until 1879 to be considered a national holiday for Canada, and then took until 1957 to have a set day! Historians claim that Protestant religious leaders wanted the holiday during the middle of the week, in order to get people to go to church and give thanks to God – which also gained Independence from Britain. Other people believe that it was a day to give thanks that we were spared having to go through what the US did with the Civil War. Even further, it was said to be a possibility of when Harvest Time happens – then again proving existence of God and life on Earth through the growth of crops, Etc. It was thought to be decided upon on a Monday, in order to make it a long weekend, thus urging people to want to get on the railroad and spend money going to see their families.
Obviously this is moot bc of the massacres of the Native Americans for being forced time and time again to run and or fight for their rights, only to have them consistently taken from them as their family amd tribe members were slaughtered in front of them, only to be expected to adhere to these laws mads up against them.
I recommend reading Black Elk Speaks and The Sacred Pipe, but there are a multitude of historical references you can easily find on the history of Thanksgiving in Canada and the United States and how it effected the original people living there beforehand as a result. Be mindful.