It is by normally the convention for the "Segunda Punta" not Trequarsista wears No 10. However, it is also common that segunda punta to be the most talented player in the team, hence No.10 also stands for representing "the best player" in the team. Nonetheless, in modern day I think No 10 connotates more with the fact of being the most "talented and technical" player and thus should be given to one that best fit the description. That is why Zizou and Totti wears No 10 for their respective country despite the fact that they are no Segunda Puntas and should be wearing No 8 in traditional term (Well Totti can be one that is beside the point).
Anyway, No. doesnt really matter unless you have a susperstition in which case it may affect the performance through phychological effects. Other than that, I really don't mind what number people wear.
Having said that, I would also give Canna No.5 in the international team because in International matches giving jersey is one way of telling what you expect from the players but in club games it doesnt really matter since he would be seeing Don Fabio on a daily basis.
