No, you can not sponsor him. If he is under 18 and you want him to come and stay with you and go to school, you could apply for a study permit for a minor child. His mother would have to sign that he can go and you would be appointed as his custodian. As a foreign student, he may or may not be covered by health care. I do not know how that is in NS. Because he is a foreign student, you may have to pay tuition for him even though he is still in high school or lower.
There is another option if he is under 18, father dead, abandoned by mother and uncle possibly having problems to let him stay and that could be to apply for a TRP for him on humanitarian grounds. If he lives in Canada on a TRP for 3 years, I believe he can apply for PR.
If he is older than 18 and wants to go to college, he would have to apply for a study permit, show funds and pay his tuition.
If he is older than 18 and wants to work, he needs a job offer and a work permit.