I am also preparing to apply for PhD in Marketing programs in US and Canada. I am not sure how consultants will help because it is quite obvious what you need to do make your application more competitive. Here are the things that I have learnt so far:
1. Good GMAT Score (700+ will put you in the consideration set in top universities, for B category B Schools you need 680+)
2. Good GPA (The more the better, although I had a low undergrad GPA I have a tad better graduate GPA which may or may not suffice, I will find out later)
These two things will put you in the consideration set (shortlist set). Then comes the qualitative parts which are:
3. Statement of Purpose (You need to show what you want to research on and match that to the professors in the university of your choice)
4. Letters of Recommendation (From your past professors)
Thats about it. If you can do all the above you can hit the nail on its head.
Good Luck! to both of us