My fiancé and I have been together for 5 years now and we moved into our own place last April so we are now considered common law, will we have to file for income tax together or can we still do it separate??

We live in Canada and have an 8 month old son together.

Also, if we do have to file together will either of us be losing out on money or will I lose my child tax benefits or gsts I get for my son?