Who does/should cover for a mother out on maternity leave?

When a mom goes on maternity leave, how is the work covered at their place of employment when they are gone?

This is top of mind to me, as I will be taking 14 weeks maternity leave when this baby comes, and am already training an assistant to do a bit more, and handing off work well in advance to take the burden of my absence off my team as much as possible. 14 weeks doesn’t seam very long, but if I was taking 9 months I am sure my employer would have to cover my role in a longer term way... so, I wonder what happens in other places of employment? If you are paid on your maternity leave, are the people covering your work compensated differently because they will have more on their plate, or is a temp paid to help?

I am especially interested in responses from Moms who are in countries with longer extended maternity leaves (like UK or Canada, etc) because the solution is needed for a longer period of time, but all are obviously welcome to comment on how it works for them.

I posted this in CC because I see a lot of people discuss maternity leave (or lack of) here, so I thought there would be some good conversation.