Boss forcing me to comit to overtime?

I have a newborn baby at home.i told him I will do overtime but cant comite to certin days cause if my wife needs me,ill have to go.he didnt care,insisted I give him 2 night at least.i tried explaining how im tired from lack of sleep and how my wife needs me home to help.i told him I would do overtime but cant say the days I can for shure.he insisted I comite to 2days..telling me he males apointments for our clients(im a mechanic)and how stupid he will look if he has no mechanic.i told him I have a comitment to my wife and new born.he dosnt care...remember I didnt say no to o.t,just qhen I can ill stay if im needed at home ill leave.he forced me to give him 2 days a week of ot.never mind my family..now we are in quebev so its quebec laws,,,also I have proff hes forcing me..what should I do?i need my job...last guy that went on paternal leave during our busy season got fired(oh he took them to court,was even in the newspaper and radio telling his story)