I have incurred legal fees to try to reduce the amount of spousal support I pay; is this expense deductible?
No. Legal fees are only deductible to the person asking for support.
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns206-236/232/lgl-eng.html