Assuming that copyright law is the same now as then, are we safe to assume that JS would keep the US copyright and that HE assumed the whoever bought it in Canada would not dick around with the content?

Sorry if it's super-basic but it's been rattling around in my head. Not a great way to start a religion.

Oh well, some revelations are.....from Satan?

about what the copyright purchaser would do after selling the copyright in Canada.

AFAIK, there is nothing in the historical record, including the first-person accounts of David Whitmer that suggest that there was any concern other than getting some money out of the sale of the copyright.

Theoretically, I suppose that they could have negotiated contractual terms that would have restricted the new owner of the copyright. But that would have so undermined the value of the copyright that it would have been even less attractive to any potential buyer. As things turned out, they couldn't find an interested buyer in any case.

If they had successfully sold the copyright, the new owner would have been able to change the contents, would have been able to make derivative works (e.g. putting heroes like Moroni into a negative light, as adulterers or criminals) and could have prevented the sale and distribution of the book by the Church later on. Eventually, it would have gone into the public domain, so it would not be permanent. But the fact that Joseph Smith was willing to sell it all is an indicator that he wasn't particularly concerned about it as being a book "containing the fulness of the Gospel of Jesus Christ." (This is further reinforced by the fact that Joseph Smith rarely, if ever, quoted from the Book of Mormon in his sermons and preaching.)

The attempted sale of the copyright in Canada is clear evidence that the "Book of Mormon" project started out as money-making venture. They hoped the book would be popular and a steady source of income. That was "Plan A".

Only later when it became clear that it wouldn't really sell as a book that people wanted to read, Joseph Smith converted it into a gimmick for selling a new religion. That was "Plan B". He had much more success with Plan B. than with Plan A.

His family was starving at the time so he had to do something. Although I have to wonder why his neighbors disliked him so much they wouldn’t feed his kids.