well i think that you should train that player for your own team and not go for the U21 cuz canada is a big community and there are many managers who can train their players for the U21 NT.
first of all u have a good level trainer(i hope u arent paying much on his salary).
just start by pumping his OD to proficient(i would have done that to prominent) then follow it up by training him in handling,JS,passing and driving all to proficient.
then work on OD till prolific or sensational and then train him in JS and handling to prolific.then if u want u can train him in some inside skills (especially IS and if possible then train SB too cuz it is quite effective for guards)....
then come back to guard skills and u can train him in any skill u want to train.or u can rotate OD,JS,handling,passing and driving so as to get a pop in each and in the meanwhile you shall also get one or two JR pops.