I'm no expert on all of this, but it's my belief that some TFSA's are trusts; some are not. I had one a few years back (which, mercifully I cashed out long before I had even heard of this US tax issue) for which every year the financial institution sent me a statement of trust plus annual transaction activity. I believe one in which you can hold stocks, mutual funds, ETF's or other investments would definitely be a trust.
I have one now that sends no such paperwork; only a simple statement of interest paid just like any other savings account. Because it is tax free in Canada it doesn't generate an information slip like a regular account and doesn't even appear of my my Canadian return. (Funds contributed to a TFSA are after tax dollars, create no deduction from income when they are contributed, gains within are not taxable, and funds withdrawn are not taxable.) The account is listed under one account number along with several other accounts with the same institution.
For US purposes I add the income from all accounts under that account number and report that on Schedule B. Whether or not I'm doing it right I have no idea, but at least I can't be accused of failing to report income. That's the trouble with trying to serve two tax masters; the two tax codes do not mesh with each other. With the IRS nothing is ever simple.
Thank God the only mutual funds I own are within RRSP's and covered by the 8891's. The IRS should really allow TFSA's to be reported in similar fashion, but it will take decades before they get around to it. I have rearranged my finances to make US reporting easier, but I resent being denied some of the strategies which other Canadians can take advantage of. And all of this ridiculous reporting to produce a $0 balance return every year.