You signed a sponsorship agreement with CIC, re-read it.
You and your partner signed a sponsorship agreement that commits you to provide financial support, if necessary.
This agreement also says the person becoming a permanent resident will make every effort to support her or himself.
You must provide financial support for a spouse, common-law or conjugal partner for three years from the date they become a permanent resident.
From the form IMM 1344
Basic requirements include food, shelter, clothing, fuel, utilities, household supplies, personal requirements and health care not provided by public health, including dental care and eye care.
I promise that financial obligations or other personal circumstances over the applicable period referred to above will not prevent me from honouring this agreement and the sponsorship undertaking I signed or co-signed;
I promise that the sponsored person and his or her family members will not need to apply for social assistance benefits; and
I promise to respond promptly to requests for help from the sponsored person and his or her family members by giving money, buying items or providing services for their living expenses.
OBLIGATIONS OF THE PERSON TO BE SPONSORED
As the person to be sponsored, I promise to make every reasonable effort to provide for my own basic requirements as well as those of my accompanying family members;
I promise to ask the sponsor and co-signer (if applicable) for help if I or my family members are having difficulty supporting themselves or meeting their own basic requirements.
LEGAL AND FINANCIAL CONSEQUENCES
The co-signer, if applicable, is jointly and severally or solidarily bound with the sponsor to perform the obligations of the sponsorship undertaking and is liable with the sponsor for any breach of those obligations. If the sponsor and, if applicable, the co-signer do not provide support as required, the sponsored person can take legal action.
So if he claims social assistance benefits you are liable for them.
