We all know that Roast Turkey is the canonical dish in both countries. Cornbread figures prominently in the Southern US.
What are the other significant differences?
From my experience, there are no major differences between Canadian and Northern American dishes. We have most of the normal Turkey (or Goose/Duck), yams, potatoes, stuffing/dressing, pies etc... There are probably more differences with in the United States itself (southern vs northern), for example the cornbread you mentioned.
In other words, when I watch American Thanksgiving food/cooking show specials, the large majority of the dishes are very familiar and relevant to my experiences up here.
I would suggest that most variations come from families' countries of origin/culture.. For example, my mom usually cooked some special Chinese dishes, but clearly that isn't a Canadian thing. (Also, Southern influence, coastal influence, Latin influence etc..)
There are many regional variations within the United States. In Miami, where I grew up, we always had Cuban style black beans and rice. Friends from Haiti would add Haitian dishes. My family in Georgia would have dishes that were unique to the South, etc.