if she will sponsor you from here it will show more genuineness of your case it will be better to sponsor from here as it will save the cost of going Canada.
if your case is genuine they might not even ask you for interview and you will get visa more sooner than you expect it may take as you might see from
www.cic.gc.ca that talks about average times for particular cases your case is strong your interview will be waived don't forget to send them joint bank statements and DNA tests of your baby to prove that baby belongs to you two.
wish you all the best