How are "best weeks" determined for maternity leave?

I figured people on here would probably know so I won't clog up the online inquiry form to the government!

I work on an hourly basis and my hours vary a lot week to week. I get paid monthly. Based on my economic region they use my best 21 weeks to calculate my mat leave payments.

Does anyone know if they will just look at my monthly pay stubs and average to a weekly payment, or if I break down my hours by week for them?

Thanks!