According to
this MSDN blog post[
^] from 2007,
bigint
values are returned as strings, because there was no cross-platform support for an 8-byte integer type in
variant[
^] values.
The posts suggests that this would be fixed in a future version. However, a comment from 2010 says that it wasn't fixed in 2008R2. Another comment suggests that it wasn't fixed in 2012 either.
It looks like you're going to have to change the SSIS parameter type to string, and try to resolve the problems you had with that approach.