Try to keep the scan quality of the scanner to only 200 DPI then if the file still large , use ilovepdf.com or pdf.io to shrike the file even further.
I suggest you try to cut down on some documents, for example , if you are not claiming work experience in Canada you do not need to submit tax declarations at all, it's completely optional and can be substituted by bank statements showing your available funds. However, If you feel it will support your case , try to speak to the local tax office and ask them if they can offer a brief statement that shows roughly how much you made and paid back in taxes over whatever you want.
As for bills , again , IRCC doesn't care if you paid electricity bills or telephone lines as long as you can proof your business exist through a trade licence or professional practice permit then you are good to go. you can take them out and substitute with either first and last month bills. Keeping proof of payments by customers is important and can act on behalf of your expenses to show that your business is legit.
With all of that, you can really bring it down to well below 4 MB.
Regards,,,