Hi Kevin
Glad to see OMFS is still your original aim.
Just like the others said, your MD will not give you an edge when you apply for OMFS programs in the states, especially having completed the full 4 years after dental school and not the other way around (which is Harshdeep's case). It won't hurt you but it won't be what makes programs eager to take you.
In my humble opinion, if OMFS is your main goal, you should have opted for the internship spot you got. By going through med school you are kind of "leaving the field" a little bit and that is never a good thing in the eyes of program directors.
6 year programs in the US will not accommodate you unfortunately and as a matter of fact you might become a less desirable candidate for them, because they would have to make adjustments to their program in order to take you on, which is not something that any program director wants to have to do. Your best bet will be 4 year programs.
However I do not understand the comments made with regards to licensure in the US. You can be a board certified oral and maxillofacial surgeon with a 4 year degree and you do not need an MD or an internship in Gen Surg. The only downside to being a 4 year OMFS graduate is that some states will not allow you to perform cosmetic procedures unless you have an MD (aka rhinoplasties, malar implants, botox etc...), mind you these are not even the majority of the states. So yeah... Not sure where that licensure comment is coming from.
You can still apply to OMFS after med school, but I think you should prepare for an alternate choice by externing/doing some research and building connections in fields such as ENT and plastics. Just in case you do not get into OMFS, at least you would still be a desirable candidate for those other specialties (and mind you, as a DMD applying into ENT, you are very desirable).
Best of luck buddy, enjoy Quebec city