I thought the undertaking is for 20 years so parents won't even get OAS before 20 years have passed.To get OAS, they have to be a resident for 10 yrs. Any disability benefit will be considered as welfare benefit and you have to repay that. They are not eligible for any other types of social benefit (like social housing also).
Depending on your province, they will be eligible for (almost) free drug and dental benefits.