Hi,
This reply is probably too late but I am also applying for a work permit for my postdoc position and have been advised by my institution to choose the LMO exemption. I think this should apply to all postdoc positions. This is where I got my info (click on the "obtaining a work permit" section): w w w .sgs.utoronto.ca/postdoctoralfellows/Pages/International-Postdocs.aspx
So, did you get your work permit yet? I'm anxious about my application because I'm supposed to start work in 2 months but the processing time at the LA office is supposedly 3 months (I just submitted my application early this week).