as I remembered you said you are using SUN and IBM technologies, SCA is also an IBM promoted technology.
I am also eager to know what is the relation of SCA with lazy loading here, I know how you can solve your problem using SDO, but I can't understand the relation to SCA.
In addition, if I get it correct it is a "single" 3 tier application, not a application  that need to be connected to an existing legacy one, or giving service  to some unknown external applications. if this is the case SCA will be a heavily over kill solution.
you said you are using EJB3 and JPA if this is the case Seam will solve your lazy loading problem very easily, without need to change your architecture  by going from JPA to SDO or putting an SDO wrapper around your JPA