You cannot *sponsor* your brother-in-law for a TRV. You can only invite him.
Your invitation letter must specify the duration of his visit, preferably exact dates if possible + purpose of his visit. Your invitation letter does not mean you are legally responsible for your brother-in-law after he arrives in Canada
If you suspect your brother-in-law is likely to overstay his visit or breach the conditions attached to his TRV.... then do not issue an Invitation Letter or other documents as the host
