Via the NFL site, here's an interesting stat was explained for which the converse does have implications for the CFL.
In the last 10 NFL drafts prior to the 2016 NFL draft, 61 quarterbacks were taken in rounds 4 through 7.
Only 17 of these QBs (27%) have thrown at least 50 passes in regular season play in their entire NFL careers. Of those 17, only two have become starters: Tyrod Taylor of Buffalo and Kirk Cousins of Washington. Another two, Bruce Gradkowski and Matt Flynn, have been steady as backups over the years.
And so 4 out of 61 QBs (6.5%) drafted in the lower rounds in the prior 10 drafts are even steady NFL players!
Note as I have stated and cited previously in a separate thread, by no means are even half of the current NFL starters and overwhelmingly most backups fine CFL potential in my opinion.
Even so such recent experience in the NFL draft means that CFL should continue to have a vast pool (perhaps over 90% of them), via also these drafted QBs in the lower rounds, from which to pull its prospects.
No doubt many such QBs will do their year or two of well-paid practice, training and clipboard duty and the like in the NFL, but remember there is always a new draft class of QBs drafted in lower rounds and various free agents who can do that as well and often for even less money.