How can a US citizen get a year-long visa in Canada?
If your sister wants to be certain of avoiding the ire of Immigration Canada, the path seems simple: (1) Mr. Canada files immigration paperwork for her under the family class as a fiancee. (2) She lands (3) They get legally married and start planning the “church” wedding. Having separate legal and church/big-party weddings is common with international marriages.
Re: deborah’s story: do not attempt to cross the border WITH HOUSEHOLD GOODS as a visitor. You can perfectly legitimately enter as a visitor, but if you’re bringing your wagon train, they’re going to want you to be in an immigration status, i.e. already having applied for permanent residency from outside Canada and received your paperwork back. And, since you won’t be married yet, immigration won’t be automatic, as deborah points out. This is not what you want. So if she wants to just go live with him, she has to do it as a tourist, without household goods. Leave her household goods in storage or Mom’s basement or something.