I own a small web design company based in Canada and have been working with an American company on some websites we have come to the agreement we would like to be partners. The basics is I need to own part of their startup company. A newly formed incorporation for the purpose to own a few websites I will build in exchange for the ownership in part of this American company.. Some other thoughts were to:

Draft up a contractor agreement/contract?
Buy voting shares in this company?
Become a full on US citizen and own that way.

What are my options here and any advice is welcome.

Thanks in advance!