Quantitative Marketing is very closely related to Economics, it's mostly the use of Economics to study Marketing questions. So, I see a background in Economics as a positive thing for Quantitative Marketing. It's pretty common to see marketing professors and students with a background in Economics.
Of course you need to find a better motivation to do Quantitative Marketing than "the current deplorable state of the econ job market." This makes you look like a person who is not motivated enough about marketing issues, and motivation is important (not only for applications, but during the PhD).
About schools, I don't know Canadian schools, but check papers published by faculty that are related to your research interests. If the research fit is good, you should apply. Since you are only focused on Canadian schools, the number of schools is much more limited, and maybe you should apply even if the research fit is not that strong. That doesn't mean applying to schools you have of intention of going to.