Because Canada is a nation distinct from the United States. The same reason why New Zealand is a separate nation from Australia (or vice versa).
Canada would gain nothing, and lose a great deal by becoming a part of the United States.
It's not like it happened by accident. Canada fought the War of 1812 to stay separate from the US.
The chances of Canada being invaded by the US are non existent.
It was an agreement between Great Britain and the US that detailed the boundary between Oregon Country and Canada.
Canada is a separate country, it is not part of the US but is the territorial neighbour to the US in the north just as Mexico is the US' southern neighbour.
The lakes that separate the United States of America and Canada is actually called the "great lakes". There are not these lakes across the whole border of Canada, because most of them are more to the east. If you have noticed, if you put all the great lakes together, they spell "HOME".
Great Britian
1782. Britain did not separate from US it was the US that separated from Britain.
United Kingdom aka Great Britain
The chances of Canada being invaded by the US are non existent.
Great Britain used to own both of them.
Great Britain hasn't ruled (owned) Canada in quite a long time. So realistically they cannot give Canada to the US. I can't imagine Canada joining the US voluntarily either as we enjoy our society and way of life to much to give it up.
Great Britain and Canada.
The War of 1812
Medical Services
Great Britain
Great Britain, Netherlands, France, Spain, Russia.
Britain has had nukes for a long time. After World War 2 the US shared its nuclear technology with Great Britain and Canada, and Britain developed into a nuclear armed nation.
It is a Treaty betwee Great Britain and the US that establishes the border between Canada and the US in what was then called the Oregon Territory.