If you graduate from a US law school, you will need to get your degree acredited by the national accreditation burreau in Ottawa, then apply to the bar in whatever province you want to practice in.
Also, when considering salaries, you have to consider cost of living. If you are making a decent salary at a Bay St. law firm of 100 000$ you will live like a king. But even with a higher salary in NYC, you will live in a shoebox. However, the opportunities to make BIG money, in the million dollar range, are probably much higher in the big US cities.