Hey GG, Ive got a few notes for them too. Did Theismann only play a year for the Argos? I think he played 3 years actually.
http://www.pawling.net/theismann.html
And thats a picture of Armstrong playing against the Toronto Argonauts!
To answer the above question, there have been players going back a fourth forever essentially but the degree to which this has happened has varied over the years. In the 50s the CFL paid more money and people like Billy Vessels and Bud Grant and many others came up for the money. And players like Johnny Bright were coming up for racial reasons too. Later the money evened out and the NFL started paying more but still players like Joe Kapp and Joe Theisman came up and started their careers in Canada.
You have to remember that there are significant differences between the games and different kinds of players tend to excel at each game, so often players that dont quite fit the NFL mould come up and develop even further and then catch the interest of the NFL again. In recent years this would describe Jeff Garcia and Doug Flutie, neither of whom fit the NFL mould but who both became very smart successful QBs in the CFL and were able to transfer that experience and leadership ability to the NFL too.
Even in the 70s, though, top NFL players were occasionally coming up for money. Dan Yochum was a 2nd round draft pick of the Eagles in 72 but came to Canada and never went back. Tom Cousineau was the #1 overall NFL pick in 79 but came to Canada before returning to the NFL several years later.
Moon and a number of other African American QBs came for racial reasons but I think Moons level of success in the NFL really opened peoples eyes. In recent years Garcia, Flutie, Vanderjagt, Joe Horn, and Shelton Quarles have all gone to Pro-Bowls as well, and that catches peoples attention too.
You have to be careful when evaluating CFL talent for the NFL, though, because of the differences in the games and the players history w.r.t. durability and other issues. They key differences are that the CFL field is 11.5 yards or over 20% wider, and we only have 3 downs to get 10. We use an extra receiver/DB too but for the RBs, QBs, LBs, DEs and everyone in the box, the number of men is essentially the same but the field is a whole lot wider. This means that open field players, guys who can use that space do well, while the power backs dont because of the 3 downs. Almost all of our QBs are scrambling type QBs and our best backs are the very quick and fast, but quite small by NFL standards. Overall we have superb athletes and very accomplished players, Div. 1 all-stars, Heisman Trophy winners and nominees, but they tend to be the smaller quicker type players. This is just a very general rule of thumb and there are lots of exceptions.
There are a 101 stories for how a player gets to the CFL so Im sure all these factors make these guys hard to scout for NFL purposes. Armstrong, of course, is not small at all. He is a good sized very fluid athlete with very good hands and good but not great speed. His hands are a big part of what made him a very good CFLer because in 3 down ball drops are very costly. Obviously his size and athleticism didnt hurt him any, but we have a number of better overall CFL receivers who are quite a bit smaller than he is, so the size is nice but not essential in the CFL game. The NFL game on the more compact field is quite a bit more punishing so size and durability and the ability to take hits like Armstrong took and still get up are quite a bit more important. So Armstrong has a skill set that has made him a very good player in both games.
So whats his story then? He comes from Jasper Texas which I was told by someone on this board is a bit of an out of the way place in football terms. He played JuCo ball there as a QB I believe and then transferred to a Division 2 school, the University of Arkansas Monticello. He put up good numbers there but Im guessing that thats not a heavily scouted school. Many CFL teams hold FA camps in the US to find players and the Roughriders are no exception. Some of the players who show up at our camps are walk-ons and some are invitees. We have the best GM in the CFL (who incidentally is apparently the first African American GM in pro-football anywhere) and how he finds some of the guys he does I have no idea. I dont know whether Armstrong was a walk on or an invitee, but we worked him out at one of these tryouts and offered him a contract. This is the calibre of player that our GM Roy Shivers seems to pull out of thin air. We get most of our player other ways, but these camps have turned up some real gems for us.
Anyway, Im a bit of a rambler, as you can tell,

but thats it for now.
PS-Players almost invariably love playing in the CFL. Players only have to practice for 5 hours per day so they have some extra time during the season. (There are only 9 teams so you play every team two or three times per year and you can watch all the games on television. Players still watch tape but its much easier for them to keep up with the other teams.) And its also a very fun brand of football. Doug Flutie, for example, has said a number of times that the CFL put the fun back into football for him. But given that you can make from 5 to maybe 20 times more money in the NFL, for most players there is no real choice to be made. Although its sad to see them leave the CFL you have to be happy for them in that theyll be able to take care of their futures and families in a way that they probably wouldnt be able to if they stayed in CFL. That said, if you have a long CFL career you can put away some decent money. Our top QBs now earn around $250k US and the top 15% to 20% of the players will make roughly $90k US, and up. Its not NFL money but it sure beats a lot of other things they could be doing.