If you qualify to apply under the skilled worker program, you can do that. If your occupation is not on the list of favourite 29 professions, you would need a job offer (AEO) or a valid work permit that is still valid at the time you get your PR and a permanent job offer to accompany that.
You do not qualify to apply under Canadian experience class yet because you need 24 months of skilled full time work. If you are currently working in a skilled position, you still only have 15 so you need another 9 before you can apply.
One more option is checking if your employer can sponsor you under the provincial nominee program in ON but then you must also stay with that employer until you get your PR. I doubt they will be jumping at the chance to sponsor you if you are currently on maternity leave and they do not really know if you will come back.
If you want to change employers now, your new employer needs to apply for a labour market opinion proving that they have tried to recruit Canadians or PR's and haven't found any as well as they are paying market rates. If they get the LMO, you can apply for a new work permit. Once you get the work permit, you are no longer allowed to work for the old employer, only the new one.
