https://www.natmatch.com/dentres/stats/2017applstats.pdf
This year only 4 applicants of 223 positions offered were from Canadian dental schools. I'm not sure how many applicants applied from Canada to make up those 4 people though. So according to those numbers it appears that a little less than 2% of positions are filled by Canadian students. So not knowing how many Canadian students applied I can't tell you your exact chance of being accepted, but it does appear that graduates of US dental schools are extremely heavily favored.
