Someone owes me money but there are on welfare .my question is can I get them check gaishrn every month to repay the debt.

No.

You appear to be using US terminology when referring to a Canadian Citizen.

Canada's equivalent to social security is the Canada Pension Plan. While CPP cannot be garnished at source, most recipients have their CPP entitlement direct deposited to their personal bank account. When the funds are deposited they become the personal property of the recipient and cease to be CPP. At this point the funds in the bank account can be garnished. CPP is not welfare.

Welfare benefits cannot be attached at source or in a bank account by statutory provision,

There appears to be a matter of principal here. You are owed money and should be paid. Unfortunately, it may cost you more than it is worth to get it back and take an very long time.