There are blogs you can google that claim that the tax difference is barely anything, but they never give you the math they are using.
First of all, the difference between a 46% tax rate and a 40% tax rate in dollars paid is 15%, not 6%.
Secondly, high income earners in places like Florida have tremendous deductions that aren't available in Canada (mortgage interest, and lots of other things)
I may have overstated it. This article shows it being $2.6M in tax, vs $2.2M, or about 18%, for Josh Johnson in 2012, but I think it increase at higher levels
http://www.forbes.com/sites/kurtbadenhausen/2012/11/14/traded-marlins-players-will-take-2-million-tax-hit-in-canada/#4e87b7a3b2f1