I liked Dalhousie quite a bit when we visited. It is in an attractive area not all that far from downtown (you could walk), but not exactly downtown. My daughter was looking for a smaller university which is why Acadia and Mount Allison were more attractive (as was Bishop’s in Quebec, which is closer to where we live). Academically these three schools are all very good and probably do not differ much. Universities in Canada are consistently very good. Dalhousie, being larger, will have a larger range of majors and a wider range of classes. I think that it is a very good choice.
Given that you have Canadian citizenship, the universities in Canada should all fit your US$20-30,000 budget. I am not sure whether your listed GPA is weighted or unweighted. If it is unweighted (ie, nearly straight A’s) then some merit aid is possible. In our experience merit aid in Canada is generally very limited. However, when the base price is only about US$20,000 per year (including tuition, fees, room and board) it does not take much merit before you feel like you are getting a bargain at a very good university.
I am not sure how difficult it would be to get residency in the US after doing medical school in Canada. I have heard of it being done and one of my specialist doctors here in the US got his MD at McGill. Certainly medical school admission is competitive for everyone. One advantage with Dal is that it has a good medical school and connections with hospitals in Halifax.
Two things that I have noticed since we have a daughter at university in Canada (who graduates very soon): She seems to have more classes in her major and fewer “side electives or unrelated requirements” than would be the case in the US. She has been getting into specialized classes that would probably be graduate classes in the US. Also, as a dual citizen attending university in Canada, the biggest risk seems to be that you might not choose to return to the US.