Wouldn't you think that the best WRs from the CFL would make the jump to the NFL a bit more often if they really were that much more talented than the bottom of the roster guys. I guess to some being a #1 on a CFL team is more prestigious than a #4 or 5 on an NFL team. If I had more time I'd look into the salary differences.
The salary differences are huge. The CFL team salary cap last seaon $5.7 mil CAD, or about $4 mil USD. With 45 man rosters that puts the average CFL salary at about $89,000 USD. The highest paid player makes about $750,000 per year.
Reggie Begelton's salary at the NFL rookie minimum (plus a $2,000 signing bonus) would make him among the highest paid players in the CFL. 17 weeks worth of NFL practice squad checks is well above the CFL average. I don't think it's a matter of CFL players not wanting a shot at the NFL. Not many are asked to try.
The NFL camp per diem is $1,700 per week, and if an ex-CFL player gets cut just before the start of the NFL season he'd miss about half the CFL season. He's probably pretty good by CFL standards so a job should be waiting north of the border if he gets cut.
I think there there are usually about 20 or so ex-CFLers in camps, maybe a half dozen, fresh faces each year, plus or minus. A few make the bottom of a roster or a practice squad. I want to say most don't get an NFL job. The only ex-CFL starter in the NFL right now that I know of is Duvernay-Tardif, an OG for the Chiefs. There might be one or two more.
Guys end up in the CFL because they could not land even an NFL practice squad job coming out of college, so the bar to get to the NFL is pretty high. Late bloomers, I'd say, but quite uncommon.