I'm sure there have been players, even some very good ones, who made it from the CFL into the NFL. I don't think Sams is that kind of good as a player. I could be wrong. But, yeah, this is being blown out of proportion for Sams' sexuality, not his skills as a player.
As for Jackie Robinson, most NL and AL players start their careers in the minors. Those who are good learn and move up, as Jackie Robinson did. Having him in Montreal avoided a lot of the separate facilities crap that would have complicated many minor league teams logistics. It was a shameful reality; in that respect there is no parallel to Sams. IOW, the Sams-Robinson analogy isn't analogous.