It is not possible to create an equivalent to your C# structure in Labview.
What Labview creates will be something like this:
(C++-Syntax)
struct TPCANMsg{
unsigned int ID;
char MSGTYPE;
char LEN;
LVArray** Data;
}
struct LVArray{
int Length;
char Data[1];
}
You also have to check that your dll uses 1byte struct member alignment. This is what LabView expects.