I looked at that Canon scanner and got mixed information. When you bought it, did it have the film scanner accessories? If not, it is a document scanner and will not scan negatives. The issue is that the scanner is designed to work with reflected light from the document to a receiver near the traveling lights. With the glass negatives, the light passes through the negative and then reflects from part of the negative and from parts of the white upper plate.
Film scanners have light from the top shining through to the receiver on the bottom. There is no double reflection. I don't believe that what you have has that top light function. If you have the film scanner accessory, then that either has a light or has some other way of not getting the double reflection.
Here is the US, we could probably rent a film scanner for a couple of days. I'm not sure that is true for where you are. If you are in a business and will sometimes scan film negatives, you should consider buying a film scanner.
Have you considered trying to put a black background behind the glass negatives and then taking a photograph of the negative? That may be better than what you have if you don't have a film scanner. Once you have the image, something like the free GIMP may be able to reverse it. I'm never tried this.
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BoilerPlate: To posters who ask for help -- it is nice to thank the volunteers who try to answer your questions !
Anything I post unless stated with a reference is my personal opinion.