i think more than anything - its situational. No one player is going to leave one league, and single-handedly dominate in another league, without the other 10 or 11 players he is surrounded by making a large difference in his success (coaching included, players are often misused). Comparing individual performances from one league to another is just stupidness - and further underlines the football ignorance of those making individual comparissons.
Ricky Williams, is a good example of this .. Had he been given an offensive line and 25 carries a game we may have seen different numbers. Who knows?!
Had Ricky Ray been on any other team than the Jets .. he may have had success as well.
How good can your allstar wide receiver be, if you have a loser throwing the ball? How great can your allstar running back be if the Oline doesn't block, or your play calling is terrible? How great can your allstar DB be, if there is no pass rush? Football - more than any other sport is a team sport ... and individual success can be accredited to team efforts, not just the individual.
sure there are CFL players that can cross over given the right situation ... the vast majority cannot. Fact is - playing professional ball, in any league, at any level, is chalk full of politics, favoritism, right place at the right time, depth situations, and making the most of an opportunity ... HUNDREDS of great football players never make it to a professional level for dozens upon dozens of reasons .. injuries, fell thru the cracks, poor teammates .. just because its the NFL, does not mean there are not errors in their selections.
success is not an easy thing to find in the game of football, no matter where you are playing.