CHOPPER, to qualify for a US license your TC license must not show any restrictions. In other words you can not be limited to "daylight flying only" in Canada - as the FAA does not issue a commercial rotorcraft license with out a "night rating".
You should then pass the first or second class medical (depending on your requirement) second class is equivalent to our cat 1. If you have a canadian medical and a heart beat you will pass the faa requirements!
You must then take a recognized ground school course, which will be signed off by your ground school instructor, this sheet must be presented so you can write the exam. Multiple choice, right out of the study guide.
The FISDO office will recognize your candian commercial and give you a faa private rotorcraft license. This is required so you can act as pic on the checkride.
You then complete the minimum required 3.0 hours of dual training so you can be recommended for your faa check ride. The flying is the easiest part of all!
If you do the training in the states, you must first be accepted for training in the US by completing the required faa Oklahoma screening, making sure you are not osama's cousin.
It takes 3 to 8 weeks for the screening, 2 to 3 days to do all the rest...
Best of luck,
VR
