No particular order on these three guys amongst those who are the best receivers in the CFL:
As implied in the article the chips are down on any given receiver from the CFL, or any given free agent otherwise, making it to be a backup in the NFL without having solid special teams skills that emphasize more than just pass-catching.
Great discussion below citing the importance of special teams versatility for the NFL for receivers, but note that this reality also applies to DBs and LBs who are not good enough to start. Good points below by Earl as well.
By contrast note that some NFL starters with amongst the best special teams skills in the league are kept purposely off special teams, unless it is late in the game and the team is way behind in some cases, due to high injury risk. See Devin Hester and Dez Bryant, with the latter having been played for sake of punt returns one time too many last weekend though with little or nothing to be lost for sake of next season either.
Otherwise I don't see one potential NFL starter who is not already on the field right now, and at any given time other than for injury or suspension these guys looming out there are few and far between.
However, for some guys like Fantuz there are situational roles to which they can be adapted such as on 3rd and long, multiple sideline routes to force space and match-up problems, and with his height also for the red zone. The ability to snatch the ball out of the air with good-sized hands is key for these guys irrespective of not having blazing speed. Note also that in many situations of certain field position, route running skills and lateral agility make a bigger difference than just speed.
Note also these guys have to overcome the higher physical nature of the NFL off the line in the bump zone of five yards.
Above in my opinion are the CFL players still deemed young enough who could play in the NFL in certain situational roles such as the above. Note that with the looming NFL lockout for 2011 anyway, it's now or never to give it a go anyway with nothing to lose in the process.