https://en.wikipedia.org/wiki/List_of_hardy_palms
I actually left out the concise point i was trying to make in my earlier post that is actually is possible to grow some kinds of palms outdoors in the Detroit - Windsor area just barely u need to protect them in winter with a burlap outer layer and a mulch interior if i remember the advice from a (Windsorite?). This actually goes for many areas of the northeast and midwest however technically a small area around lake st clair and the detroit river of the metro area where the water tends to keep nigh time lows slightly warmer in the winter that theoretically some of the cold hearty palms could grow without protection. I don't think it would go well though because while some palms can grow an do as far north as the Tennessee and Ohio Valley's but while maximum night time low temps may be the same a 6a in climate zone terms. While it may drop to -10f in Nashville it wont stay that cold for an extended period like it can in the great lakes region, but to me its a really interesting idea to me at least to think that there is another place in Canada other than Vancouver that the cold heartiest palm trees could theoretically survive i.e. it's southern most tip.
Edit*(I didn't notice that north 42 had already expanded on to the point i was trying to make which makes the previous addition a little bit moot, but thats what i get for trying to post on my Iphone haha. But i felt it was important to expand on what i was sayin but at the same time temper it by adding in that while the lakes protect certain areas from getting the kind of extreme low temps that the rest of the region is known for during its coldest winters and of how odd it may seem to be able to grow Magnolia's and other cold hearty "tropical" plants in small pockets of SW Ontario and SE Michigan and the West Coast of MI all the way up to Glen Arbor. However as mentioned before if you do want to grow cold hearties in this area you need to be mindful that while for the most part the marine influence insulates certain areas as we all know once you think you've seen it all in terms of weather here that's when you will be surprised so an eye to the sky is needed so to speak and protection in certain extreme events may also be necessary)