Many of the first people of what is now known by many as the United States prefer the label of "Indian" over the label "Native Americans".

A very excellent (if also very "edutainment") exploration of labels and the label of "Indian", based on conversation with people who identify as "Indians", can be viewed here:

https://youtu.be/kh88fVP2FWQ

The proper way to refer to the indigenous peoples of the America is honestly a pretty complicated topic. "American Indian" is still generally considered valid. In some cases it may even be more correct, like when referring to indigenous peoples from outside the modern United States. It's typically preferable to name specific groups though, as indigenous peoples weren't homogenous. Just "Indian" is pretty outdated, but you'll occasionally see it on things with a lot of historical baggage, like the BIA.

The term appears to be almost as offensive to Canadians as the n-word is to Americans.

Sarcasm or not, your post is racially insensitive, hence the downvotes.