There's talk about adding new states these days. The territories aren't even in US jurisdiction, but that hasn't stopped it before. An example of that is the annexation of Texas.
By the way, all of this is based upon memory of how it was taught in school back in the day when I was going to school in Texas.
Texas was annexed by JOINT RESOLUTION in the US Congress. Sam Houston preferred a treaty, but a treaty could not pass the US Senate. Indeed, an annexation resolution passed by only ONE vote. There was a sectional controversy going on in those days, and the North opposed it on the grounds that Texas would join the Union as a slave state. Not to mention the fact that Mexico threatened war if the USA annexed Texas.
The Resolution passed anyway, and was sent to the Republic of Texas for approval. There was a popular vote taken on it, and the people of Texas approved. But what may not be commonly known, the President of Texas, Anson Jones, worked with the Mexicans to add an option to the annexation vote. Mexico offered to recognize Texas' independence if Texas would not join the American Union. The people of Texas voted the Mexican offer down, something like two to one. Upon annexation, there was a war, and Mexico lost. The Mexicans also lost a lot of territory in the West which eventually became the states of California, Arizona, New Mexico, and not to mention the parts that Texas claimed ( which was a bit of stretch) that included the modern states of Colorado, Kansas and Wyoming.
There was significant consequences of the annexation. Civil War came just 15 years after Texas entered the Union. The annexation aggravated an already touchy situation in the United States. That's because a lot of territory was below the Mason-Dixon line, and the South wanted more slave states. California joined the Union as a free state. This was one of many factors why the South wanted to secede from the Union. They were losing power in the Congress. In particular, they were losing power in the US Senate.
So what's the point? The addition of new states by Joint Resolution is precedented. It can happen again. It can also bring about a lot of unintended consequences.
Greenland cannot be a state. As for Canada, if any part of it joins, it's going to have political consequences that may not be forseeable at the moment. If Alberta joined as a territory, that might be a better option. Statehood could be decided later. Even though it is legal under Canadian law to leave their union, there would be a significant question of what to do about the lands in Alberta, and who owns those lands. Would Alberta control all their territories, or would the Canadian government claim those lands?
There might be a possibility of Alberta joining, but at the moment, I think their answer to that proposition would still be a "no". I'd be just fine if that were the case. However, if Alberta joined, then who knows what will come next. More provinces joining up? I wouldn't like that one. Too many unanwered questions.