When the NFL expanded ~15 years ago adding Baltimore, Jacksonville, Houston, Carolina, there was a huge drain on available talent in the CFL. Prior to that expansion the argument of leagues' relative talent level was less profound.
The Canadian college system plus import quotas ensure some really good talent at certain positions, notably linemen, some defensive back positions and occasional receiver. The NFL expansion talent sponge grossly affected CFL talent level at quaterback, receiver and safety - defensive backs; still present today.
The game's rules develop some dramatically different play strategy. American players, college and NFL, are awestruck at the physical fitness required of CFL players, often shadowing CFL players to learn their training regimen; a few who played both leagues have published books or chapters on this aspect.
It's not just the bigger field. Clock rules are hugely different: less time between plays; average ball in play NFL game 11 - 15 minutes, CFL about 20 - 28 minutes ball in play. These 8 - 10 minute drives much praised in NFL are impossible with CFL clock rules, there's never been one in 90+ year history of the game. Different sets, one yard line of scrimmage offset, more man coverage although this changes with teams and seasons, tight end (NFL) vs slotback (CFL). NFL excels in specialized player utilization i.e. 3rd down receiver or lineman who only gets on field for 3 - 5 plays per game, almost absent in CFL.
Where the league's really differ is NFL tremendous vs. CFL's modest talent level and NFL's moronic and intrusive clock managment rules vs. CFL's less intrusive, less stoppage and time wasting play. NFL game 3 - 4 minutes left leading team can essentially run out clock; in CFL that's impossible until about 30 - 40 seconds remaining.
I think it's the CFL's clock management rules that engender endless comments of how the Canadian game is more exciting despite modest to bad player talent.
