Ask the neighbour’s Contractor provide evidence of insurance which names you and your property as an additional named insured.
Ask for the Contractors City of Toronto License number, to make sure that he is a licensed contractor.
Contact your house insurance company to let them know that the neighbour is working on the attached house and that some work will be on the shared wall, and that you are being asked to provide permission for this work.
Ask the neighbour’s structural engineer to copy you on his site inspection reports, so that you can be informed about the progress of underpinning work.