I solved such problem a couple of times very succesfully by:
- put masking tape left and rigth of the seam to protect most of the canopy from scratches
- scratch away the seam very carefully (scratch from front till aft) with a very sharp razorblade or X-acto knife
- remove the masking tape
- polish the canopy with tamiya polishing compound. This is the most difficult step; if you put too much pressure then the canopy might break
the whole process should not take more than 10 minutes
lots of success